I don't really think Magnezone really restricts my teambuilding process that much (1 free moveslot handles it? Yes please) but that is just me. Not to mention that literally half the tier checks it
you say it handles maggy but I really don't see how P2 alone is handling it. And I REALLY don't know what proygon you're using because analytic specs T-bolt has a high chance of 2HKO (both boosted of course) after stealth rocks. Meaning that if P2 is forced out once (takes a volt switch into something that wont let it recover, or the slew of things in the tier that have knock off. The next time it switches into magnezone (unless it gets a wish pass) then its dead meat in most cases. While I can see it kind of dealing with some magnezones I don't see which ones are going to stay in on a P2 taking less than half since P2 can recover stall and even ones not running HP ground can chip away with shadow ball or tri attack or whatever.
You went kinda out of your way to deal with something but I don't really see it consistently being an answer for magnezone though the game, just based off how common knock off is and the many popular things that force P2 right out and can work up volturn synergy forcing you to switch the half game.
assuming you don't also have a ground type to block volt switches, magnezones will most likely do this. (which would bring your one move slot counter into 2 whole pokemon counter) Personally using magnezone I love to set up situations where the opponent has to switch or lose a pokemon. And then volt switch away from any potential non-ground counter, if there is one however, I'll take a risk at HP ground if my opponent is switchy, it comes down to prediction and magnezone is never really on the bad side unless hes locked in by a magnezone countering magnezone (fast with HP ground) but that still takes two pokemon to set up (inefficient magnezone and a ground type)
To address hazards once more; one of the main reasons I don't think hazards or spikes are a very large deal to magnezone is that hes so efficient at theatening most hazard setters in the tier
on its own. Once they're gone, all you need to do is defog (or spin) This is on top of already being resistant to stealth rock which is much more popular than spikes because of all the fire types and flying types that are hit harder than they would be by spikes. Not to mention stealth rock's superior distribution.
Sp.Def mew is 2HKO by T-bolt and very harmed by volt-switch, mew can knock off specs but that does nothing to set up hazards. The predicted knock off could be abused by a switch in. (openings for megadoom are yummy, among other things) Since mew has not much else to do on magnezone, burning is counter productive and hazard setting would make him dead.
Nidoqueen is 2HKO'd by flash cannon and the way it's speed is creeping it out speeds non-invested queen.
Foretress can be 2HKO even by flash cannon unless it runs specially defensive. Tbolt OHKO's p. defensive overcoat sets.
Aerodactyl is OHKO'd by anything other than HP Grass
Even sp.def MAggron is 2HKO'd by Tbolt, if it hasn't evolved yet, the only chance it has is sturdy on a clean switch in.
for the sake of the post size I'll stop here but the list goes on and on, some of the most popular spikes and rock setters shiver with magnezone around. even if I don't believe residual hazard damage especially from spikes matters all that much in balancing when it affects everything grounded. Does something need to be ground/steel/fighting +levitate to get banned?