There will always be complainers for guns.
If everyone has it how can some people say it is unfair? Everyone is at a level playing field if everyone has one. If it truly was unfair then it is your own consent to handicap if you don't use it.
There are many guns you can use to best the modeus and there are even alternative PM weapons that can be just as good (MP7 / Veresk).
Not saying that the Modeus isn't amazing; It is one of the best guns in the game but not so much that it deserves a ban. If you want to complain about easy guns then might as well complain about the m4mk3. Super easy and also 'takes off the creativity of a rifle man'.