I'll leave out that assault and support need to go back to how they were in BF3 or 4. Assault should be ammo guy, support should be health guy.
Aside from the total rework though, I'll say for assault like for every class, the passives should just be always active instead of needing to unlock them through score. I actually opened the game to give a fair run of the passives. Breacher is more grenada, reduced penalty for shooting while moving, and 15% faster reload for assault gadgets. Grenada one is actually good, but make it 2 more instead of only one. The penalty reduction... I don't know, that's a hard one to really identify in game as being useful or not. I don't know how you track that as a dev either, can you filter kills when that passive is active and compare it against other kills that aren't getting that? That's how I would decide if it's actually a benefit, and work it from there. Nothing wrong per-say with it, just don't know how to identify it as a player. The reloads? Eh, puke. 15% faster reloads for everything would be a good change. Frontliner tree... squad that spawns on you or beacon gets 2s of adrenaline, less falling damage, and faster health. Again, adrenaline is multiplying by 1. And for 2 seconds? The fade in takes 1 second, so... yea. Change that to squad can spawn on you in combat. Bam, instant improvement. Soft landing. Wow. I don't know man, this is garbage. Maybe change this to vaulting and similar actions are 15%-25% faster. This I could see as actually having some real benefit. Health regen I would say is really good, maybe lower those values and add that it can start faster as well. Rally squad active... I guess this could be ok with a buff to the adrenaline effect, but I would say it's just multiplying any number by 1. No real buff doing that. I honestly can't think of an easy replacement to make the active shine.
Gadgets... the class gadget epi-pen just sucks. I understand it got a bit of a buff in recent updates, but unless that thing gave you some REAL buffs it's always going to be worthless. As it works now, you get just enough time to sprint into a room and die to a TR7 or SCW in 1 second. Kind of useless. If maybe it offered some health, or a much longer duration, or maybe if it worked as a self-revive, all those could give it some real use instead of just being an untouched button. I assume you track gadget use by players, how does it stack against all other class gadgets? Boom GL is a lot of fun, but has little real utility and almost no counter play. It's most effective being used like a shotgun, to kill 1 player at a time. More destructive force, maybe being extra effective against other gadgets would help it actually have a legit use. Fire GL is a joke, it's useful to... ehh... I have no use cases for it really, it just sucks. It should operate to flush enemies from cover, but since it deals about 2 damage for all of 2 seconds, AND doesn't have a good visual effect to make players want to avoid it or get out of it, just blech. Ladder is PEAK, but almost worthless gameplay wise. If the ladder could actually take some hits and not just break from a tickle it could really help the thing. Fire shotty hot garbage, and not literally the hot kind. Make it a regular shotty that you can choose ammo for (Fire, buckshot, slugs, boom, darts). Spawn beacon is an extremely useful tool. I don't think it needs any changes aside from maybe some nerfs so it's easier to find, but even thats kind of ehh. I think that's all gadgets? I would take the mammoth pack from support though and give it to assault, lengthen recharge time, remove ability to heal from the thing. Lower the recharge time for GL as well, they're 1000x less useful than launchers and launchers recharge way faster, should go the other way around. I forgor the penetrating flash grenade. Thing is actually kind of fun, but since only soft walls can be penetrated, it sucks. Give it another charge, let it REALLY penetrate, OR if it can't pen then have it still operate as a sort of sticky flashbang instead of just essentially being a dud.
Grenades. Since frags are all, nothing to care about. Stuns are ok, but they need more of a movement penalty and a little bit more duration. They also should decrease hipfire accuracy if they already don't, more if they do. Flash... man, those things suck. If someone isn't staring at the thing it's a dud, and even if they are you have about 1 second to take advantage of that blind. I would increase the length someone if blind, AND shunt their aim somewhere else when they get blinded. If I'm aiming at a door when I get blinded, I can just spray the door because I know I was aiming at it, and likely remain safe until I'm not blind. Count on those should start with 3, passive give you 5 as well. They should recharge faster from packs too. They should be a great pick to engage a guarded entrance, but I never see people use them over just running in CoD style and gunning people down. I never use them unless I've been drinking and want to play like a rat.
Weapons for the class... well, I think that carbines and SMGs need a range nerf, and assault weapons need more accuracy and distance. As the game is balanced now, there's no real reason to pick an assault wpn over carbine or SMG aside from the tiny buff you get from the class passive. I don't know if that's an assault thing over just game balance thing though.
Assault is supposed to capture OBJ faster, right? Well, it really doesn't feel any faster than any other class, and a buff I would give it is that it can cap OVER an enemy who isn't assault on point. So 1 enemy and 1 ally on flag, if one of them is assault and other isn't, OBJ should slowly go towards assault team over non-assault.
As it stands, assault reads like it should be the Delta force, easy company, go fast go hard kind of class. But it plays like every other class with worse gadgets. Assault weapons should be a "good for almost all engagements, but never great" but instead they feel like almost every other weapon in the game.
It would be really funny though if one of 1/1000 chance things was instead of using the epi-pen, assault took a drink of a red bull. That'd be funny.
TL;DR The assault class doesn't shine in any aspect of play. Assault has no gadgets that feel like they make a real difference. Assault weapons are lackluster. Grenades are lackluster.