You say all guns don't have to be usefull, but hell, in SG 90% are useless.
9mm, 10mm, sawed shootgun and normal shotgun should stay poor weapon to start and have your first hand on. I don't even speak of zip gun and pipe rifle that are useless even to start and against rats.
You speak about flamer, yeah but flamer are required for BG to lv, i saw many guys with it, cause it's range is low, but dom are insane and against all cac bots it's really good to lv, like the 10mm pistol, so no point here.
Then you should have upgraded weapon, a bit more usefull than the first ones, deagle, magnum, grease and tommy gun and maybe combat shootgun.
But here we have already some issues, tommy gun is really crap. While grease gun is not so bad, high dommages but low range, he could be used as a shootgun, tommy gun is completly useless, if you want to snipe, you use a hunting rifle and his burst is inferior to grease or 10SMG, not to mention than bursting at 32 distance is useless.
After that we have the main issue for tier 2 with AR and FN Fal, where normaly you should have a bit better weapon than on tier 1, you have expensive and useless things.
I think 10mm SMG is not at his place here, since it's supposed to be the really first SMG to use, but in fact, it's stronger than AR in burst ... maybe putting it at 4PAs was not that great, don't know ...
Caws should be here and for AR, he s not good compared to 10smg, 1 more AP and ammos are worse (10% dr more on 5mm) maybe make it burst 10 bullet and wide a bit the magazine to make it interresting, same for the ext mag versions.
FN Fal is the first rifle of the liste interresting, it has good stats, good ammos, but impossible to get, almost. Maybe keeping this way is a good thing, but actually 7.62 are really too rare to be interresting, you don't want to get thoses high end bullet for midle game rifle :/ So this weapon become of some use only to craft the HFPA (which is tier 3 and not avaible for the most of players)
On guns, now 14mm and needler are clones, only difference is magazine size :/ Before 14mm was too expensive for what it does compared to needler, but now they are the 2 same guns, adding poison to needler would be fun for exemple, and give the penetrate perk to 14mm instead. (I will not speak of needler ammo change here :p)
Finally tier 3 have the champion P90c, great range not much ap, burst mode, cheap ammos, decent domm. Pancore that leak range, in Fo2 pancore had 35 rang in single, 25 in burst, it was clearly a bit too much (30/20 for caws and 22/18 for combat) maybe put something between, 25/16 could be a good deal, leting users shoot at correct range in single, low range in burst.
XL70E3 is supposed to be "upgrade" to AR and he have exactly the same weakness, doing less dom than the basic FN Fal :/ Someone proposed to make it indestructible, it could be a good idea, make him deteriorate really slower than other guns, but not sure it'll change anything to effectivness. So maybe simply do the same things than for AR, put the burst to 10 bullet and eventually wider the magazine. One thing is fun with this one, you burst by 8 and have a magazine of 20.
Maybe i forget things, i have tryed to be as clear as possible and give some ideas.