It's hard to see an implementation that doesn't end up being "find the strongest thing in your class list and spam it", which to me kills a huge part of the appeal of both character building and the combat system.
About "inventive play", it is in fact explicitly allowed and encouraged. The game never says powers only do their described mechanics and have no further effects, and IIRC the specific example of fire powers setting fire to things is mentioned as up to what the DM thinks makes sense and wants for their game. It provides both mechanical guidelines and advice on what to consider when adjudicating actions beyond the character sheet specifics. I firmly believe the game is better when played this way, and I don't think that's an unusual opinion (or would be, if the matter was discussed more).
Its flexibility and robustness are big parts of what's great about 4e. It allows for a wide range of interpretations, can handle inventiveness both before and during game time, and when you can't or don't want to improvise and invent for a while it just keeps trucking along being perfectly playable and enjoyable to just do what the book says until you feel like getting more mentally involved again. I think that's really cool. Of course, if you don't enjoy this kind of board game combat your mileage will vary.
tl;dr: 4e is as open to imagination as any RPG, and when imagination dries up you still have a fun board game to fall back on.