As I told Sintax, at least for me the main matter is the lack of explanation about why they had those illegal moves. And it doesn't help when, in many cases, LEGAL moves would do the same job (or better), without being, you know, illegal. By example, giving Zangoose Nightslash instead of Cut. Sure, it loses 5 potency... and gains improved critical chance, and it is totally legal (Fake Out doesn't have any equivalent, though, unless we use Fling with King's Rock)Again. Your own mon have illegal moves too. So actually, you can do what your enemies can do.
Now, if you don't really know how to play pokemon you should not complain about illegal moves either since the game IS balanced.
If it was explained, as in "those mons were experiments from Team Creation or were affected by said experiments", to give an example, at least there would be a reason IN game about why you don't have access to those moves on those pokemon. And your waifumon are aberrations, which explains WHY they have those moves. If there were another waifu gardevoir from the same experiment, teoretically it would have the same moves as yours. If we face other modified mons, even those that we won't have access, it wouldn't be illegal moves if those mons moveset actually includes those moves.
What I found hilarious is the fact that, according to the PBS last time I checked it, pupjaw HAS an illegal move in the first fight, and one designed to make the first fight less of a lottery, when it would be easy to just give it to his moveset and make it legal XD
Ultimately, the game IS unfair. Not hard, you have the tools to beat, even crush, the trainers, but unfair, and without any explanation in story about it.