I know that I can be frustrating to be in a sit where you know the other person is in the wrong but they can just make up some bs and you have no evidence to disprove it.
But at the same time leaving it all up to the server would make it unplayable; the lag occasionally gets bad enough but adding more and more thing may help f1s but the lag created as a result would fuck up the server.
As many people have said before, use plays tv... I am able to record on a "ok" laptop at 1080p with a half-decent frame rate.
And I highly recommend making a config for gmod, it really helps on shitter set-ups, and tweaking with your setting and possibly even lowering your resolution will most likely boost fps by 10-20.
Also recommend pasting this into your launch options for gmod: -console -nojoy -high -threads 4 +mat_queue_mode 4 +r_hulkalloclightmaps 0 -dxlevel 90 -window -noborder