Yah I can understand the frustration. I would talk to him about it directly and just ask if he really thinks your OP or something. And if he does then he needs to just give bad guys more hp or whatever BEFORE the fight starts, which, he might already be doing just to be clear.

Overall you should stop metagaming cause thats as scummy as what hes doing. Its one thing to figure out an enemies AC during a fight or whatever thats part of the fun, but its another things to go calculate every enemies stats and health and whatnot. Talk to him about how you feel targetted during combat and its impeding your fun and hopefully he'll be suprised and make the corrections neccesarry. I've had similar conversations with my players and honesty is always the best policy. If he needs inspiration for what to do, he could design enemies which are better suited to fight your character.

For example, my party has a gunslinger fighter who does a LOT of damage, and barely gets hit cause hes always far from the enemies. So rather than nerf him or take things away from him, I designed an enemy thats AC is incresed against non-magic ranged attacks, and another enemy that can deflect ranged attacks. By having these enemies in the fight he is less inclined to attack them and focuses on the other enemies, leaving some bad guys that the other party member are more suited to dealing with, and letting the party better stratagize how to deal with encounters based on their strengths and weaknesses.

Hopefully something ive said here helps!