It depends on what your definition of "competitive Pokemon" is
If you are only interested in the battles, then no, as you're not giving yourself an advantage that somebody else wouldn't be able to obtain. For instance fighting games often have codes or some sort of mode that unlock everything, so nobody has to waste time before they can get to playing the game.
If you consider the whole cart experience as the game, then yes, genning is obviously cheating, you're using unapproved means outside the game to achieve your goal.
Either way, nobody in charge of these things cares and nothing is going to be done about it, so like
stop worrying about it, breed if you want to breed, let genners gen cause they're gonna do it whether you like it or not
Pokemon is a trash game anyway
