This thread has a spreadsheet with the odds of finding a monster type in the top three kingdoms for each monster type:
Dwarves in Khaziel appear with a 1.14 probability. That means if you play “a lot” of battles, you can expect to find about 11 dwarves for every 10 battles.
So “one or none” is the result you should expect the most in Explore. If people had a reason to set their defense teams to be dwarves in PvP that would be a good option, but the devs are complicit with the current setup that encourages people to use the same 2-3 teams or else they lose their PvP ranking. Think about that next time your finger hovers over a button that might send money to the game.