You are totally right that he is frustrating and sucks the fun and progress out of the game at times. I have been so angry at being stopped on a bunch of friendships by him being crazy OP!!
I think for the campaign : Ursula needs to Hex him so Yzma turn him into a llama, Gaston soak up the bear traps, then when Mr.I comes back to human you red potion him?
Gotta remember: He is also really helpful to a lot of players! In our guild MrI mercs that are vital for lower rosters to complete CW, or clear levels in Surge. He is a hammer for a lot of campaigns.
I think there are ways around him; a couple tactics that have worked for me in the past: if they are available to you(not always possible in friendships!)
Hank &Dory can swing in and blind and offer a slap/stun
King Louie can both move him back& sap and his memory disk will automatically slow him if Mr. I is the last one standing.
Syndrome and Buzz can bubble him but inconsistent.
Rajah is great to suck up his punches and drop a beefy hit, microbot to get his attention also.
Merlin,Genie,Facilier have transmogrification.
Rapunzel w/best day ever disk can whallop him to the back and slow him down.
You could build a team that focuses on nerfing his bd? There are some interesting combos that will reduce bd if slowed, armor stipped,etc.
Maximus has taken a silenced&Studied Bob Parrs best punches and spit apple right back at him!
Stitch(Ma) has a great slow and enough damage to make a difference.
Olaf is pretty durable and gives good constant freezing. K&S help lock him down, and the heal can get you back if he manages to get one rocketpunch off before you freeze him, or if he gets loose.
The new MadMadamMim refresh gives another hex option that could be helpful, especially since there is a passive that could be very useful against those fights where the computer starts the battle half-cocked and ready to punch your face right away.
Sorry your going through a tough patch! I hope you are able to break on through and finish your Friendship Campaign!!