You aren't coming off as hostile at all!
I've played against the deck with my Atraxa, Karametra, Mina and Denn decks (which are all my most dialed in decks), as well as a few other ones I've tossed together. I already have the reputation of making decks that aren't fun to play against (Atraxa has a bad rap just because I run a semi-reliable land base, Karametra has some soft stax effects, but nothing too oppressive, and Mina is essentially a Valakut deck with some land destruction), which is why I've avoided going full Stax. I don't want to build a deck just to try to slow down Mizzix. It's easier for him and I to just play one vs. one games with other decks.
Again, if I'm actually playing a multiplayer game and he uses Mizzix I wouldn't care at all.
I would also argue that combo decks in a one vs. one setting tend to perform better than in multiplayer. Dealing with only one players worth of counters or other interaction is way easier.
