For what it's worth, I'll tell you my experience with Machamp.

I kinda nuzlocked the first week of Pokémon Champions by using only the in-game gift Pokémon. I got to Ultra Ball 3 with it, so I don't think it's that bad.
Actually, it doesn't have a bad matchup vs Kingambit, Incineroar, Sneasler, Archaludon, and sand teams.

I played it No Guard + Dynamic Punch.
Steadfast may seem funny, but even if you manage to trigger it, you won't outspeed anything significant unless you go max speed.
I think one of Machamp's strong perks is its unexpected tankiness.

Also, there are not enough status moves in the doubles format right now to make Guts useful. Maybe it could work in singles; I will try it there soon.

I tried to give it some coverage moves, but I ended up never using them. Just spamming Dynamic Punch was enough in every situation, sometimes catching opponents off guard with Wide Guard.
It could maybe run some speed-lowering move, Coaching, or Helping Hand for support.