for real... are all the weapons in the game useful?

it depends but i think they are useful

well m249 is pretty bad and useless to be honest, why would you buy it when you can buy cheaper, more superior gun in negev

The most useful weapons in competitive are these:
M4A4, M4A1, USP, Tec9, MP7, AK47. Why not AWP (but only if you are good with it).

nono who the fuck needs the mp5? its just a bad version of mp7

All guns are good in their own way, depends on how you hit the weapon and their utilize their spray patterns.

A lot of guns do have their uses, certainly moreso now than older versions of csgo but some guns are too but to justify using e.g mp5sd when you can use mp9 and personally the ONLY pistol I ever buy is a deagle. Personally the one tap potential at all ranges and the two body shot kill (as bm as it is) is too good to give up for inaccurate dink machines.

yes ofc bro i like this game because im from poland

No, the negeb, aug , ssg is not usualy, shotguns too

No, you have maybe 8/9 weapons max that you use in competitive