Cut =/= not able to finish.
And if you can only finish half a game in 5 years someone needs to step in.
Regardless, The Phantom Pain doesn't have half of it missing. Chapter 1 is a complete experience, on its own more than enough to be a game. Chapter 2 is a shoddy, hacked together anti-climatic mess that ends the game on a sour note, and that's on Kojima.
I honestly think chapter 1 is filled with filler missions, just like GZ had those extra ops.
I'd like a shorter game but with a good chunk of story missions (and with story missions I intend missions actually bringing usefull info to the player with cutscenes, like Hellbound was, in example, or Skullface etc) instead of a 100 hours product in which you visit the same outpost 100 times in order to extract a prisoner, find a plan, fultoning a special soldiers.
Even excluding side-ops, a lot of main ops are here just to fill the game. To me, it was clear there should be other location in the game, not only two. But they couldn't achieve it and, in order to create new content, they created those missions because honestly they are very easy to do, you just need to change some variables and that's it (this, of course, excluding intro mission dialogues etc, you actually need to recorder those, but by a gameplay point of view, those missions are very easy to create).
This excluding all side-ops, that also recycled dialogues and they only change the placement of some items (like spawn X tanks in 32.5Y and 89.1x).
Actually if they used a script, they can randomly generate side-ops easily, making an infinite amount of them.
If extra ops were fun and good in GZ, because really we bought a demo, here, but extra ops provided additional hours of gameplay and they were different enough to be worthy to play, in TPP way too many main ops are just "Extract this dude, blow up that thing."
I had (still having) a lot of fun with the game, even if it's literally filled with issue and I honestly don't understand the praise from the press (and this by being a hardcore MGS fan, this is my favourite franchise), but it's clear the game suffered a lot of issue and the final product feels incomplete and its length artificially increased.