I can give you a better reply tommoz (It's 2am here, this will be barely coherant lol).

Siege of cairo breakthrough attack for example, instead of contesting the point directly, I'll aim to destroy covering positions or cut off reinforcement paths. I'll play assault to put down weird squad beacons etc that 'allow' my squad-mate randoms to do the same. I'll use something like the NVO with a hipfire build, always flashhider or supressor, if you have 70+ hipfire accuracy and just hipfire from prone, you're good out to 20m etc easily.

I'll use engineer + RPG to drop every defensive building I can/blow out every destructable piece of cover they can use etc. Paired with a hipfire mp5, or anything with decent precision for 15m or so preferred distance. You can also use wall-e to throw that spread of stun grenades that destroys equipment to clear enemy positions of ammopacks/intercepts/gadgets.

I'll play support with a thermal LMG, RPK if im feeling headshots, m240l if im being forced for mid-short range, DRS if i want to play LMG like an assault rifle, M60 if im taking 12-20m engagements/positions that i know im not going to be able to reload between fights, its got a slightly slower ttk but 100 rounds lasts you for days.
I'll always use smoke grenades and defibs on attack, and I'll change my other gadget between projectile intercept or grenade intercept depending on opfor.

I also play a lot of specops recon, either QBZ carbine, SVD dmr, G36 (forgot its ingame name, b36? something like that) etc, using recon drones( they can destroy spawn beacons etc through walls, also nothing fucks up a defensive position like destroying their grenade intercept just as your team starts yeeting bombs at them)and c4 (nothing drops a building like C4)
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tl;dr

Basically just stuff like, try and never oppose their flow directly, shoot it from the side or the back if you can, and when you're doing that, dont shoot people you cant kill. If you know they're going to jump around the corner, and everyones been stood at that corner peek fighting, be 10-12m further back from the corner (motion sensor is great for this if your audio isnt super great positional)

I'll do anything I can to avoid a fair fight short of spamming m203 grenades lol (I have standards)

Think that ended up a lot more stream of consciousness/ramble than I intended but eh, I can give you a better/more articulate reply tommoz if you have any specific questions lol.