For one, I don't think it's a 'gamble'. It's something that the game design clearly intends for fighters especially to do. If the game traps you for doing something it encourages, it's bad game design.
The game does not encourage one fighting style or feat over others, and when it comest ot feats the game actually encourages ASIs.
It is not the game designers that encourage these hyper specialized builds, it is the white room optimizers.
It's also a problem that doesn't exist for casters. There's no "wand master" feat. The closest that casters get is probably "elemental adept" which overcomes the problem of resistance which would be the equivalent of caster specialisation.
It is not damage, but then damage is not the best metric of power. Casters have plenty of extremely powerful feats.
Metamagic adept is pretty darn powerful (although not spammable). I would say Warcaster is pretty close in terms of being an extremely powerful martial feat.
Really though Fey Touched is probably the most powerful feat in the game, letting a caster get an off-list spell, Misty Step, niether count against concentration cast it for free once and then spam it. Hex, Dissonant Whispers and Command being three awesome spells mechanically. Because Dissonant Whispers usually causes AOOs on a failed save it is a very effective spell from a damage point of view too.
Shadow Touched is also very good and with Cause Fear on a Fey Wanderer Ranger using a 2nd level slot it is borderline OP.
I would put any of those four feats up against PAM in terms of power, even if you get the unicorn Halberd or Glaive.
DnD has a play time of YEARS. People develop emotional attachment to their character. Coming back to the table every week until the campaign finishes, knowing that your character concept isn't being honoured by your DM, when they have an incredibly strsughtforward way to resolve the issue...
The most straightforward way is to change your build or change how you play regardless of the sunk cost in your build.
If your DM is not letting you change fighting styles at an ASI I would agree with you. But that is fundamentally different than altering the story and plot to focus on a choice you made on your character.
Choices are choices for a reason and putting a magic polearm in a room because I chose pole arm master is akin to making a Troll vulnerable to Radiant damage because I brought holy water with me instead of acid and oil.
Two examples from in actual campaigns -
1. we walked into a study and decided to search it instead of going straight to the next room. The BBEG in the next room heard us (or maybe he was told by his familiar) in any case he escaped with the loot, we weren't abole to bring him to justice, the bad guys won that day. Shoudl the DM have fudged this and just had him attack us instead so we could have the climactic battle and go back to the town heroes?
2. My Artificer walked into a room without checking it for traps, she sprung a trap became paralyzed, enemies came out and over the course of 2 rounds was killed dead and other party members could not get to her. This was the lowest point in my 5E playing career. It was worse than the two other characters that died. Should the DM have just changed it up somehow so I would have survived.
3. The PCs were all captured and stripped of their gear (this actually has happened to me twice). In one of those we escaped through the sewer without gear and my Rogue was running around attacking enemies with a broken longsword hilt we found (as an improvised weapon). Should there have been a Rapier lying in the sewer muck so he could sneak attack?
These kinds of things, and giving a PC a specific item for no reason, would make the choices you make trivial. It would take it from shared storytelling to DM story telling and it would not be as fun IMO.
