Weapons that are never going to have a substantial impact on gameplay, because they'd struggle to kill units a tier lower or even two tiers lower.
UEF and Cybran units are particularly guilty of this, having little extra features that don't actually do anything.
UEF T3 gunship AA is so weak that you'd need 10 of them focus-firing (and always hitting) a single ASF to kill it in 15 seconds, the fight might not even last 15 seconds.
Cybran T3 gunship AA is a little better, it can do it in 10 seconds and it's missiles. Still, an experimental's worth of gunships isn't going to kill a single ASF without focus-firing.
UEF and Cybran strat bomber AA is a little stronger relative to mass, but of course strat bomber and ASF engagements are so short that there's no chance of an ASF dying.
All T2 transport weapons (all have AA and all but Aeon have a ground weapon) falls into the uselessly weak category, especially the ground guns. The one possible exception is Cybran, because a 4DPS weapon with EMP might be useful.
UEF T3 transport can actually beat an ASF in a 1v1 (but not a 1v2), or a small swarm of interceptors, so its fairly weak AA actually matters; however its ground guns most definitely do not.
UEF, Cybran, and Seraphim frigates, UEF and Cybran destroyers, and UEF, Cybran, and Seraphim battleships all have really weak AA.
Of course, these are tough units and can be escorted by cruisers/carriers which have amazing AA.
There are only two situations where this AA being so weak is actually a big problem for the player; No cruisers have been built yet and there's no air support, or it's a Salem and going places where cruisers can't follow and aircraft would die.
And lastly there's ground experimental AA and battlecruiser torpedoes.
Monkeylord and Fatboy AA is enough to deal with T1 scouts and small groups of T1 bombers. Sure, they're early experimentals, but strat bombers are almost certainly going to be a concern at their stage of the game.
Megalith is even later game and has even weaker AA, it'd struggle with singular T1 air units.
And battlecruiser torpedoes would take 30 seconds to kill a T1 UEF sub.
I'm not sure what I'm saying about what needs to be changed about the game, I think that with the exception of the transports and Monkeylord all of these units would be considered overpowered if they were buffed further.
I do think it's rather misleading to new players though to label a unit as having "AA" when it's completely incapable of protecting itself against anything you'd expect it to encounter, plus the similar situations with a few non-AA weapons.
However, these weapons should be kept as they fill an "anti micro" role, otherwise you could much more often force a player to waste APM by constantly sending units where they can deal damage without being damaged back.
Are there any units where you think it'd be reasonable to makes some changes to their minor self-defence weapons?