I slightly disagree with you here, only because you don't want to be running around with a sniper, you want a fast and easy gun to kill and move. Where as snipers are very slow and decrease running speeds.
i totally agree with you i just have something to add on:
the upgrade sniper doesn't really have lot of ammo, i am pretty sure after round 20 anyone one would like to run with a gun that cant even kill every single zombie i know its 1 shot kill and all but 50 bullets and 250 zombies hmmm..... not ganna happen