Here's my two cents.
Brawling has a sweet reward to it. But it has its place. I love AC20/10s and every variant of the two calibers. But I know that they can't be useful 100% of the time.
I've used the 2 AC20 Demolisher a few times to great effect against missile boats. What the hell can a catapult, vulture, or cougar do to that? Bail out and suck an autocannon round to its BA.
This doesn't always work, and you need a team to support you to get it to work. But once you notice that the oppoenents are getting too specialized you can go in with some autocannons and mess their world up badly.
Longtoms have their risk. Just pulling out of the mechbay on some maps is enough risk to warrant its reward. They are the most vulnerable tank in the game. A single puma can run in passive and take you out. An APC powered down behind your base can spawn a point of elementals to shred you to pieces. And what the hell do you do when ASF come out of the blue (no pun intended)?
Aerospace Fighters. Let me tell you something. If one is tearing you a new one, you're just being outplayed. Those pilots are taking the riskiest role in the game. My life expectancy against 0 opponents while piloting a ASF is about one minute. Those things are hard to pilot. Thus the reward they give should be what it is. Leave ASF alone. The counters are there and fine right now.
Missiles boats can be countered easily. If you find your brawling mech/tank getting wasted trying to get to them, you're just being outplayed. The other team is effectively using a mix of fighters to maximize their kills. This is how the game works.
Remember when you are gibbed, it doesn't always mean there is an imbalance. It just means the tactic you thought of using just isn't going to work at that time. Switch tactics. There is no one tactic that will always work or even be average all the time. What sounds good on paper or in your mind when sitting on the john usually goes to shit during a change in the fight. Sometimes all it takes a slightly different placement of a Hollander II, or someone using a PPC config of a Catapult (that you didn't see until you were dead or sometimes not even at all, "what the hell killed me?") when you thought it was a Missile Boat (done this a few times, see 3 catapults and decide to ambush them with a Puma Prime or Demolisher and find one of them is a PPC Catapult, holy hell that sucks).
One thing you cannot expect is to run to the front line, target an enemy and think he targets you back and he's the only one you have to fight, with everyone else targeting their own peeps for a group of duels... Doesn't work like that, the moment you come over a hill, everyone's focus is on you and to make you look at dirt.
Sometimes there is no variant to counter another variant. Sometimes its position.
One problem I have with players wanting balance changes is occasionally they act as if they are god's gift to a Public Game. As if their tactic or choice of mech is infallible and when it eventually fails or even fails repeatedly against something they think it shouldn't, that its a imbalance that needs to be fixed. I'm not claiming the OP is doing this. But its something to watch out for.
Right now I can't think of anything that is out of whack. I think missles, LTs, and hvy guass are fine (my preferred weapons are normal guass, PPCs, and autocannons). The only change I'd like to see the regular PPC cause less heat to the firer then ERPPCs(if it does already, then tone it up a bit more). When I get toasted ingame I switch what I'm doing. If I can't find a way to beat the enemy tactic I just go 'oh well, they've got us this round.'
The only tactic I don't like is team stacking. I don't mind players playing with friends, but when you got one clan on one side and Pick-ups on the other, its not very fun. But I haven't seen this. I think players like kicking their friends' butts.