It's a really bad idea to try to use force to get players to play the characters you want them to play.
I disagree to a point. In my opinion, it is the DM's job to set limits based on the campaign and get everyone on the same page. Sometimes this means limiting certain play styles at the table if they make the game unfun and a chore for the DM to run.
If the players defines characters in his head not by what they believe or what they feel, but by what they can do if you don't provide for those options then you are going to lose a player and maybe most of your players.
And this is not, necessarily a problem. The idea that everyone can or should game with each other is a fallacy that needs to die in a fire. If play styles are conflicting to where the power gamer's style is disruptive by bringing broken or incompatible characters, it is some times better to send them on their way if they can't adapt to the game being run.
If the player wants to play a dinosaur rider that shoots laser beams from his eyes, you need to find out how to make that work as much as possible.
Bull! you don't. While it is good to help players tailor concepts to something appropriate for the campaign, not every concept is appropriate. If the player is unwilling to play something appropriate (including play style) for the campaign in question, you don't have to accommodate them. Having them a build an appropriate character for the setting or find another table is perfectly reasonable.
However, ideally, the DM should be talking to the players upfront before anyone builds characters. Discussion should include discussing what is and is not acceptable pc concepts for the campaign, house rules and other limits.
if the player If you have a player that is a power gamer, the thing that is desirable in the character is that it is empowering and right out on the broken edge. This is imaginative play at its heart. The player wants to play a super hero and impose his will on things. If you can't allow that at your table then you've got some fundamental problems. A DM has to accept player empowerment.
The only problem is lack of communication and/or the DM and the player having incompatible playstyles, And, no, the DM does not have to accept builds that are right on the edge of being broken. The DM is in charge of how the game will be played at the table, which options are in use and how closely to adhere to the rules themselves.
It's only a problem when the other players don't like playing with the power gamer. As the DM that's what you are really worried about avoiding. If you are getting rolled by a player, then you are doing it wrong because you have all power in your hands. There really isn't an excuse for not being able to challenge a player. Yes, at times you should be tweaking the rules to improve balance, but slapping down every concept until its bland banality isn't going to make for a happy table in the long run.
Having all the power in one's hands to challenge the power gamer is not the issue. It is whether or not, constantly, going out of one's way to challenge that player makes it unfun or a chore to run the game and provide a fun experience for everyone else (including the DM).