Did anyone else feel Maria was under-utilized?

[EeveeBailey]

Personally I've never taken gym leaders (or necessarily E4) to be fighting at full power. In the stories I write, Pokemon Master is an actual title and gives its holder some responsibility to respond to crises, so all of the leaders in the League system assess the trainers who come to challenge them and award badges based on whether they feel the trainer is progressing as they should be (although some GLs do get a little more competitive, but that's their prerogative). This would also be why they don't use six pokemon; they're presenting trainers with specific situations to assess how they respond.

Yeah, but i consider that idea of the Gym Leaders not use his full power and strong Pokemon, i consider that cheating. Heck, how the trainer its prepared to fight against the Champion itself if his not taste a bit of power from what he will fight?

Not necessarily.  Can you imagine trying to take your Level 10 starter against a "full force" team of a Gym Leader?  That would be rather like taking a first-grader and trying to teach them college-level calculus!

I think part of being a Gym Leader (especially being one of the first few that a Trainer will face) is knowing how to gauge the levels of their opponents and give them just enough of a challenge to encourage them to try their hardest and really fight for the badge, without being so difficult as to be almost impossible and discourage them.  Like anything else, Pokemon training is a learning curve.  It's part of a Gym Leader's responsibility not only to test the challengers that come to their Gym, but also to help encourage their growth (and their Pokemon's growth) so that when they do face the Elite Four and the Champion, they'll be ready for it.  You can't get that kind of growth striking someone with a full-strength team right out of the gate.