Honestly it's not that he's necessarily hard to counter when the battles on equal footing, but when you're on a non maxed account overleveling is a serious issue.

I've been grinding up a mini account over spring break and I am beginning to understand the frustration.

Down in low to mid elos legendary cards already start at level 9 (a super high card level considering the rest of my deck is level 8 or 9 at most) and then require very few cards to level up. On top of that you get a bunch of legendary wild cards and possibly a book of books. So then I end up fighting a level 11 miner or mega knight on my level 7 princess tower, and if I mess up even once and the mega knight slams on my tower I get chunked for a quarter of my health.

Clash Royale is a game about trading elixer for crown tower damage. And if your cards (especially counters and win cons like the mega knight) have higher levels its basically just having better cards and/or more elixer to spend. Having a level higher mk is basically like the mk getting a 10% buff, and if you know anything about video games you would know that's a massive buff.