I agree that the game is functional.
It remains functional without feats.
Trouble is that the game was designed so the GM is equipped with monsters & challenges suited to PCs hitting a bar far below the one PCs actually punch. The idea that feats are "optional" and that the baseline should be deliberate self sabotage levels of CharOp during character creation because players rarely feel that feats or magic items are actually "optional" with good reason.
The questions are
1) whether or not it is worthwhile to forgo an ability score increase to choose a feat
That's the wrong question because it omits acceptance & acknowledgement of critically important elements that solidly cement the answer in place. Because the monsters are designed to a standard so far below even the most basic "
I should put my highest stat in my most important attrib" levels of CharOp there is no meaningful opportunity cost involved in taking an S-tier feat
(or close) instead of a +2 attribute bonus. That is further compounded by the fact that in the chance event that there is an opportunity cost it's most likely because the GM is using custom or 3pp monsters which opens the door for that player to complain that the GM
needs to give them magic items that erase that opportunity cost while still maintaining the benefits of that feat.
2) and is that true for 75 of them?
We've seen exactly zero because anything in the UA can change & there has been almost no info from wotc about 5.5 that would allow forming an opinion. Back in 3.5 the answer was
"Obviously yes, duh" but with 2014's baselines it's hard to say how many of those feats will even be worth the ink or paper used to print them
Also, as the conversation has progressed:
1) Will the leveled feats mean that the ones worthwhile are locked behind being required to choose ones which aren't?
With any luck many of them will have
additional requirements beyond level alone
2) Is it good game structure to have choosing a feat compete with ability score advancement?
Not really but at a conceptual level feats have severe problems at their core since 2014 in the way they try to graft a contradictory mishmash of 3.5 mechanics & expectations onto 2e style mechanics & expectations. That clash overshadows any answer that could be given