If Mr. X isn't a formidable, annoying, unfair, terrifying foe, what purpose would he serve in this game? Back on the PS1, they probably wanted to have Mr. X as he is in the remake, but there was no way of achieving that with PS1 hardware. Hence, in the original RE2, he's a scripted monster that doesn't pose a huge threat to the player.
If something is going to be criticized, the balancing of hardcore mode in general is the issue. I was curious and started a Leon run on hardcore. You have to have crystal clear strategies and efficiency to get past every enemy encounter in the game. It's not hard mode, it's some European Extreme or Veteran shit.
So yeah, on normal difficulty, where you can botch shit and survive, or experiment with encounters, Mr. X is a really cool element of the game. On hardcore, where you're playing the game as close to perfect as possible, he is a huge roadblock and adds an element of randomness to your run.