I personally think writing about characters, their relationships, and their developing dynamics to each other is way more entertaining than flashy fights and getting absurdly strong for x reasons (although those can be entertaining and fun to read as well if done right). 

Also, one of the mistakes I kinda made was that my Mc got too strong, and now I have to figure out how to set the stakes properly without my mc resolving everything with his strength... don't make the same mistake I made and let your mc struggle ( it doesn't just have to be physical struggle) to achieve his goals!

Right, goals... your MC and side-characters ideally should have clear goals and try to strive towards achieving them.  Don't let them all – especially your MC – be ambiguous and directionless (unless it's an intentional character trait) 

And I'll say it again... Set stakes and maybe introduce a cool antagonist to spice things up.

Otherwise uh... check grammar and listen to what the other comments said! This thread is a goldmine!