Except power level is not the be all end all for everyone. I like Gambit because of his personality, history, skill set and yes his powers at the level they are at now. I wouldn't want him to use his Death persona or go back to his New Son power levels because then he would not really be Gambit to me anymore. Besides even if he is not at Rogue's level(few are) he actually is really powerful. I mean grenade level explosions with playing cards is no joke, and if writers would let him use his ingenuity more with timed explosions he could beat most comers I would say.
As for using other characters before him in the MCU, I don't think that is required or absolutely necessary. The Fox movies have thoroughly introduced the movie going audiences to a lot of the characters you have mentioned and it has been rumored before that Marvel Studios wants to focus on some of the lesser used characters from the Fox X-Men franchise rather than the same old, same old that Fox always focused on. Gambit is perfect for that because he got almost nothing and he is one of the few extremely popular X-Men that was not used much.