Iphone X not charging while playing games and decreases performance

I’ve got the fast charge apparatus (29W type-c adapter and type-c to lightning cable). When i play games while charging the phone it stays on the same amount of battery plus there is huge drop in performance making the game lag. I’ve only got this phone a month ago and don’t expect any battery issues anytime soon. I can expect this issue with a regular 5W charger but what’s the point of fast charge if you can’t use it like that?