Crossbow Expert - although it's pretty good the fewer attacks you have compared to SS and GWM.
Charger - The damage bonus is ok but it requires constant movement.
Dual Wielder - GWM is better than Dual Wielder even before you account for the -5/+10 part of the feat.
Grappler - It's so specialized I wouldn't say SS or GWM are better worse considering how you'd likely use Grappler.
Mounted Combatant - It's awesome because Advantage is awesome but it's probably not as universally usable as SS or GWM.
Polearm Master - From a damage standpoint it's inferior, but I like the flavor enough that I think it's "cooler"
Savage Attacker - Very weak.
Sentinel - Good for control. Rocks in a melee heavy party. Even better on a melee rogue. In fact, I'd rate this the best feat for damage but it's really specialized to a melee rogue. The extra damage scales nicely, in a way that GWM/SS don't (that is, it's weaker at lower level than higher level)
I'll divide the above into two tiers: worthless and worthwhile. By "worthless" I don't mean "would have no impact if it were free" but "worse than an ASI". Worthless options might as well not exist but can still be mined for ideas for magic items and class builds--e.g. a "Savage Attacks"-granting weapon might be pretty cool for a rogue.
Worthless (IMHO)
Savage Attacks: Weaker than boosting your primary attribute, especially as you get more attacks.
Charger: Doesn't scale with number of attacks. Not really a damage-boosting option anyway, mostly a mobility-boosting option.
Dual Wielder: Worse than just boosting your Dex by +2.
Worthwhile:
Sentinel: Good for control, as you noted, at least against a single enemy. If you use the DMG variant rule on marking it becomes straight-up good for control. Your offensive application is interesting, but the feat would still play a useful role even without any offensive benefit.
Polearm master: Good for anyone, especially reckless GWM Barbarians and Paladins, because it can boost them from 2 attacks per round to effectively 4, roughly doubling damage.
Grappler: Arguably worthless, unless you read Grappler as enabling grappling of Huge/Gargantuan creatures, in which case it becomes niche. Pinning is pointless compared to proning, which unlike pinning imposes disadvantage on their attacks without giving them advantage to attack you back. Not a damage-dealing feat in any case.
Mounted Combatant: Hybrid damage-dealing and defensive feat. On the one hand it gives you advantage to attack creatures smaller than your mount, which usually means Medium creatures unless you have a Paladin/Sorc who Enlarged himself and his mount. On the other hand, it enables you to use your HP 19 warhorse in combat without risking its life, so you can boost your movement to 120' per round (Dash) or 60' with Disengage without even using your own action, thus letting you melee-kite anything of Large size or larger to death. (Medium-sized creatures could theoretically be in a place where your mount cannot go, but Large creatures are obviously using passages that your mount can use.) In addition to that, it allows you to use a lance (1d12 damage, effectively +2) with your shield,
and if you don't melee-kite and your mount is intelligent (thanks, Find Steed!) you can let your warhorse attack for up to 22 extra points of damage (+4 for 2d6+4, plus a DC 14 STR save proning attack on a charge and a bonus action attack against prone targets). You could do this without Mounted Combatant, briefly, until the enemy kills your AC 11 HP 19 warhorse that costs 400 gold or 10 minutes and a 2nd level spell slot (Find Steed) to replace, so Mounted Combatant is almost required to make using a mount in melee combat
feasible. It's a fantastic feat, especially for paladins.
Crossbow Expert: Can almost double your damage output at low levels, tapering off from there, but stacks with Sharpshooter, and removes a key weakness.
Great Weapon Master: Can boost your damage against lightly-armored foes by 50%, possibly more against weak enemies due to bonus action attack.
Sharpshooter: Can boost your damage by 50% at short range, removes a key weakness of ranged weapons (trouble shooting past cover), and can boost your damage by 200% or more at long range.
Spell Sniper: Similar to Sharpshooter, removes a key weakness and extends your range. Can grant you access to better cantrips but that's not usually a factor in choosing it.
Of all the worthwhile cantrips, most of them are about on par with GWM/Sharpshooter in desirability. Spell Sniper is weaker, but Polearm Master/GWM/Mounted Combatant/Crossbow Expert each have the capability to boost your DPR by 50% to 100%. Obviously the
best thing would be to have a GWM Mounted Polearm Master Paladin of Devotion with maxed Strength and all three of the melee feats.
Anyway, that's why I don't see GWM/Sharpshooter as outliers in need of fixing. I wouldn't mind seeing the worthless options like Savage Attacks and Dual Wielder improved to the point where they join the list of worthwhile options, but the good options don't need nerfing. YMMV of course.