1) easy weapons (viper, trac-5, sirius) are fine. easy weapons that are not actually effective (vulcan) and weapons so easy literally anyone can pick them up and immediately be "good" (lancer, gatekeeper, vulcan) are not good. most AA guns in this game are designed to be stupidly easy to use to the point that anyone can use them, and also so weak that many people need to be using them and outnumbering the aircraft they're shooting at to be effective.
there is no counter to the most common infantry class (that is also free to spawn any time), that can be transported by any vehicle, that can be placed literally anywhere including on top of aircraft and inside one-way shields, firing an 800 m/s dumbfire projectile with no warning.
most vehicles have no reasonable counter to a single, one-man aircraft that stays above/below their gun angles, can continuously fire extremely powerful weapons at both the vehicle and crew, can come from any direction, and escapes at 350kph if it really needs to. even fewer vehicles have a counter to liberators or galaxies.
the vulcan and gatekeeper actually do have counterplay, but that doesn't stop them from cheesing up fights with constant reliable damage at all ranges with even the shittiest of pubs in the gunner seat.
2) until you or anyone else comes up with a better idea that does the following...
i'm going to side with "just remove them." from the beginning i've been against adding any more ESAV weapons. i was against the gatekeeper being added to the game when it was on PTS. now we're at the point where the new guns are in the game AND the old ones, but mostly just the vulcan, are still in a shitty state.
3) again, about whether there's counterplay to the weapons.
AA vs. A2G relationship right now is essentially AA outnumbering A2G 3:1. if there are more than 3 viable AA guns for every A2G aircraft, the area becomes a no fly zone and plane people have exactly 0 fun. any less than that and plane people get to farm the shit out of not plane people, and will straight up kill the AA sources. this isn't fun because it means large balls of shit, like already nearly unstoppable zergs, are mostly immune to aircraft, but any fight without enough people to do AA will get shit on.
4) there is no counterplay to C4 when the user has some semblance of a brain, you simply cannot stop a person who will strap it to a flash or has drifters unlocked, and they will out resource almost any vehicle too. same with lancer, vortex. mana turret is an example of what i'd call a well-designed infantry AV weapon that can still be used by newer players, because it does its job well and offers options for targets to deal with it too.