I'm fairly certain other community threads get way more off-topic than this lol.
Heh, true.
Anyhow, pretend I'm talking about what I specifically want KH3 to be like when I say this stuff
it wouldn't be entirely off the mark.
I think an ideal progression system is also, very specifically, not just one that constantly gives you the short-term gratification "ping" of "yay! you leveled this thing up!" but also one that rewards focus.
What I mean, in this sense, is that although you might be leveling up 10 totally different meters (abilities, level, bonus level, obtaining new abilities, etc), you should be able to be making progress toward all of them simultaneously through the main thrust of the game.
What this means is that simply by playing more, you should also be unlocking/leveling more of everything (though obviously you should be playing correctly/intelligently/well). If you have to resort to a Water Barrel minigame to level up one specific thing and ignore all of the other meters you're filling up, the game has failed. What works in R&C is that everything is constantly leveling up as long as you're engaged in combat. I'd argue that a big problem in Birth By Sleep is precisely those goals that require you to play the Command Board or the racing minigame
at the Mirage Arena specifically, because stuff like that feels like a divergence from the main path instead of continuing momentum on that main path.
BBS and DDD both have tons of subsystems, but they work much better in BBS for the most part because they're actually integrated with each other rather than distracting from each other; in practice, what this means is that if you just keep battling and making story progress, you'll get plenty of positive reinforcement (i.e. reward) in the form of constant "yay! you leveled something up!" popups. In DDD, you kinda keep needing to switch into the Water Barrel minigame or otherwise spend tons of time in the menu in order to make progress. This is directly the result of the difference in their progression systems and the integration thereof.