Felix - your concept isn't really power-gamey in any sense of the word (primarily because forsaker is so crap).
However, depending on the definition, it could be considered 'munchkin'. Specifically based on the definition of "someone who doesn't really care about the rest of the group having fun". This isn't your fault. Again, it's primarily caused by the forsaker class, which will, basically, be unable to fit in with any moderately-magical party. Even if he refrains from attacking magical party members or destroying magical treasure, he'll still generally hold up, delay and cause problems for the rest of the party (can't teleport, dimension travel, heal quickly, become invisible etc, etc.).
Powergaming is using the rules to their fullest to create a powerful character. Your character is, typically, supposed to be a great hero. Thus powergaming is being sensible. Even some of the smackdowns around are merely powergaming - they tend to excel in one particular department and situation, while being cripples in most other areas.
Min-maxing is maximising advantages while minimising disadvantages. This is merely a different brand of powergaming. Smackdowns are the antithesis of this - min maxing produces characters with minimal weaknesses, while smackdown characters tend to be one-trick ponys.
Role-playing is not incompatible with either of the two. Roleplaying and rules-use are not mutually exclusive, or indeed linked in any way. Full stop. Playing a peasant with 6's in every stat doesn't make you a better roleplayer, and playing a character who can deal 1000 damage with a punch doesn't make you a worse one. Either character can have a good history, personality, quirks etc.
Munckinism is making the game 'your' game. Playing the game to the detriment of the other players involved, stealing the show at every opportunity, cheating, and playing to 'win' against your fellow players are behaviours I'd classify as munchkinism.
Note that these can apply both to characters who abuse the rules ("my character can obliterate the entire world, and he does! I win!") to characters who abuse significantly less tangible aspects of the game ("My character's family consist of every member of royalty around the world! And they all really like me!"). The roleplayer who constantly leaps forward to talk to absolutely everything, when the rest of the party are hungry for blood is still a munchkin. He's still ruining the game for someone.