I actually was able to max my Dragon Riders - I think I had about 40 or so of them. Let's see I remember breaking them into 3 stacks of 9 and 2 stacks of 8 (or it might have been the other way around so that is 42 to 43 of them) for the Whitehill fights (since my ArchDemons would get damaged by their Geysers).
Once you get the False Princesses, you should be able to generate as many as you can afford. I think I got like 50 False Princesses from Feline and I had about 5 left if memory serves.
They were split into 3 stacks of 13 or 14 or so and they did insane damage with their Dive and the halving ability. Plus they'd summon stacks of 10 - 14 dragons of various types.
I actually enjoyed playing them, but as has been mentioned a lot, they are overpowered. Nonetheless, I don't see a reason to change them (except maybe have the summon leadership based on their numbers and not your hero's leadership).
/C\/C\
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