I don't agree that a fourth of the game is just you climbing because I think that is looking at the game a bit too simplistically. If you looked at purely the time breakdown spent climbing while nothing else is going on (no banter, conversations so on) except lookinng at pretty vistas, yes, that's probably a fourth. But that's really ignoring the entire package in favor of the small focused approach that I said I don't do with UC games.
Just because I consider the mechanic simplistic, don't mean I didn't enjoy it when executed with how the game did it. Let's take your example with Scotland. Scotland had you travelling with Sam. So you had the occasional banter, the dialogue, the cutscenes interspresed throughout the level, just like the rest of the game. It featured heavy usage of the sliding mechanic in the beginning, lots of rope swinging and indeed climbing. It did this all with Sam at your side. It put through combat encounters, areas that you could stealth, a couple of puzzles that weren't tough but still fairly creative (which is a plus) and concludes with a fairly lengthy escape combat sequence.
Scotland is great because it combines and mixes everything up to preset a great whole package. You transition from sliding, to rope swinging to a bit of combat to some climbing and sliding, to a puzzle and combat and so on. And as I said, just because I find the mechanic simplistic, doesn't mean I didn't find it fun in the context of what was presented.
And that's really the difference in how I'm looking at it. You're looking at it individually expecting it to stand up for it self. Fine. But for me? I appreciate the traversal, rope-swinging that follows something else up. I also appreciate it when it's surrounded by other aspects of the game. So it works. It's fun.
As for the multiple pathways. I don't agree. The game presented you multiple pathways and encounters in the levels big enough to warrant them. Otherwise, I'm not sure I agree that giving the player an illusion of a choice just for the sake of giving them a choice (and of all things, the traversal) is good idea.
As for pacing? I'd say poor pacing is anything that simply feels like it's gone on for too long and the player needs a change of pace. I think UC4 has fantastic pacing because it kept me engaged the entire time through. It's one of the few games I've beaten in two sittings. Which is an impressive feat for me because I rarely ever play more then one game at a time for more then an hour unless it's a multiplayer focused title with a group of 4-5 friends.
Lastly, I think we're are pretty much destined to agree to disagree. So lets not write up length replies where we just fundamentally disagree with each other (which is what I felt I pretty much did here). My hands hurt
Taking all the parts of the game together as one experience was part of the problem I had with the game. Even during my first playthrough and even while enjoying every part of the game more or less, each those extended moments of traversal and climbing started to drag by the time they were done every play session I had was full of those segments, and I was itching for some kind of development to occur, be it story-related, action-oriented, whatever. They were flat sight-seeing sequences they left me unengaged, and once the spectacle of the given environment wore off or the novelty of the banter waned, I was just ... bored. The denouement from the action had moved beyond its pleasurable state and had gone on for too long.
And that's coming from someone who loved the entirety of Firewatch, liked what I've played of Gemini Rue, Proteus, NaissanceE, Grow Home, Mirror's Edge, etc. Those games consist entirely of what's present in the climbing segments (focus on dialogue, scenery, sense of place, sometimes leisurely traversal), but they're also consistent experiences. I wasn't bored with those games because not only did they better and more accurately convey what kind of experience they would be offering (which isn't something necessarily positive), they showed a much more cohesive focus. The deepest gameplay systems in those games are not frequently put on the back burner for extended periods in order to give the player a break they never needed or wanted. Uncharted 4 has incredible moments of action with gameplay head-and-shoulders above its predecessors, doing things during normal gameplay that other devs only dream of accomplishing then the game spends a considerable chunk of its time being really, really slow with almost no imbetween. (And yes, I'd totally say a good fourth of the time I spent playing the main game was doing some kind of simple traversal, just trying to get to the next ... something, anything if it wasn't actually a fourth or even an eighth, that it even feels that way for so many people is disconcerting, and more than worthy of note.)
And unlike a movie, video games that are dozens of hours long aren't going to be completed in one sitting, so the amount of downtime needed is considerably different. The notion that every moment focusing on the core gameplay needs to be followed up with even longer moments of secondary/tertiary gameplay (downtime) doesn't reflect that people can and will play a game an hour or two or three at a time. If I genuinely need a break from the core gameplay that is (reasonably) the reason I'm playing the game (i.e. action, in this game's case), then I can just put the controller down.
If I got tired of the combat in Uncharted 1, it was because the level design for those fights took place in the same kind of static, flat arenas throughout (similar to what you've said is possibly the problem with the climbing segments) though the aspects of the game directly tied to combat were considerably unpolished in 1, too. If I had fun in every shootout of Uncharted 2, it's because the layout of each shootout in that game was always different from shootout to shootout in some key way. 2 didn't need a chapter (or two, or three, or four) or downtime after every action sequence because the devs knew then that people were coming to the game for excitement, and it could crank out that excitement in diverse ways so as to not feel like a drag.
Uncharted 4 never builds exciting momentum in that way because of its frequent stops, and all those breaks stop being refreshing at some point and in some way since I replay the games I pay money for, during a replay is when I really felt that unsatisfying hitching in the action, even though I noticed it the first time through. Taking the banter, scenery, sense of place, visuals, music and animations all together during those pure-traversal segments made them enjoyable to a degree. However, taking the concept of taking in all elements of a game as one qhole experience rather than dissecting and assessing individual parts: I took all those pure-traversal segments together throughout whole chapters or clusters of chapters as one whole experience too, and that experience felt too full of that lax, low-impact downtime gameplay. When looking at the traversal mechanics themselves, on their own, it's a problem, and when looking at the game as a whole, it's still a problem.
And I don't get how the hypothetical branching paths with different encounters/weapons (which kind of happens in chapter 10) are "Illusions of choice," or how are they any more illusions of choice compared to those paths that are already in the game. The game managed to push the player forward at a decent clip during those open segments, so there's no real reason to expect that'd ruin the pacing compared to what we've gotten with 4.
And there's no pressure to reply I don't have enough time to feel comfortable making a satisfactory reply outside of a couple hours each night. I just wanted to see where the disconnect was between how we see this game, and how we view criticism of it. I can't accept that there isn't something this game/its devs could've done much, much better, even when taking into consideration what the developers were going for, particularly with the amounts of downtime, the climbing itself and the focus on pure climbing/traversal segments. It's something that seems merely adequate on a base level as well as a macro one.