I fully believe nemona has been holding her true power back. We haven't seen the full extent of her strength, she's trained a TON of Pokémon, so for all we know, we've just been fighting her Z team the whole time in the main story.
The greninja painting in her house seems to be hinting at something, or at least to me. Maybe her real starter was froakie, and it became so incredibly strong that nemona had to switch it out for substitute. For all we know, she probably can even mega evolve it.
I know it's just a head canon, so it probably won't happen, but imagine if you got to actually fight nemona at HER full strength. She'd probably be more of a nightmare to deal with than Cynthia lol
by Xtreme69420