Inferno tactics.

I've been playing as Inferno for ages, and I don't understand how you can gather 300 demons.
Basically, I know the answer: it's impossible... Why? Because if you just take 20 Pits and completely turn your entire army into demons (all upgrades for 3 weeks), you'll get 260 demons, and that's it! There's no one in the army except demons and 20 Pits...
I'd really like to know how such an Inferno develops further!!!

But you forgot about other heroes and their initial units?;) First, second - external outposts.... There can be quite a few of them.... In fact, demonology is a very complex matter.... but with skill, you can gather a lot of demons....
As for further development, I think Ifrits and Devils don't turn into demons.... So they remain, along with Pits and demons - is that not enough?;) Higher levels.... You can do so many things - it's scary!