speed

I apologize for the stupid question.
Is it only on WT that you can play mirrored templates?
Maybe it makes sense to launch a new tournament on a mirrored template?

Yes, only on WT (TE).
The main reason for not switching to WT is sheer laziness.
Considering that generating mirrored templates is somewhat difficult at first, and some people cannot do it at all (like me and FireToSky), a tournament on a mirrored template — especially on HeroesWorld — is practically out of the question.