The main problem with Fighting Styles is that, outside of Champions, it's a one time choice that you have to make early in our career. So people are not incentivized to take something that only comes up some of the time, even if it's very strong in that circumstance. Each character is best served by a Fighting Style that they will use as often as possible.
If every martial got a few of these, you'd likely see the more niche ones taken. If you were allowed to play for a bit to see what circumstances really come up before selecting one, as opposed to having to guess, you might see the more niche ones taken.
If there was a built-in way to swap out Fighting Styles later on down the road, you could imagine seeing more niche ones tried out and used to see which one was the best fit for your character.
The worst part about Fighting Styles is that many of them require you to give up versatility in exchange for a bonus. If you have Archery Style, you're going to try to use ranged weapons as much as possible. If you have Protection, you'll be glued to a shield, even if there are fights when using a two handed weapon is better.
And imagine being the guy with Duelist Style if the first magic weapon you find is a Greatsword, lol. Now you have a core ability of your class just sitting there, unused.*
*Let's not have this comment spiral into a debate about whether or not a DM should or shouldn't funnel appropriate gear to players- I've seen this occur enough over the years to know that many people have their opinions firmly entrenched and aren't going to change their stances. I ask that we all concede that this is a thing that can happen, and Fighting Styles don't account for it.
