Our servers have a class limit of 3 per team.
Play there or find another with a class limit/sensible players (like playstuff probably has)
There are enough servers with limits on classes and sensible players that you don't need to worry about this at all. Just hunt down one of those servers!
Sure, a lot of servers don't operate a demo-soldier limit but this hasn't even been my problem.
It's the mere fact that people have made killing demo's and soldier's a rediculous priority in their game (and this will be true by and large for most public teams whilst this 'contest' continues). To the point where completing map objective's was a basic but challenging goal, but has gotten to the point where even the slightest team cooperation has flown out the window.
It's simple things like the fact that the demo is the most effective anti sentry nest class. You uber one, and he runs past 2 sentries to go after a soldier and gets the entire team killed.
Atleast with basic achievements they could be farmed, or at such a scale that one could never effectively farm it (2004 life time kills for example) but achieve it over time (and thus avoiding general gameplay abuse/breakage).
I mean sure, this is what Valve wanted
to a certain extent. But at the end of the day it's gotten so rediculous that normal play is basically impossible.