...what's the appropriate response to minimize his dominance? For instance, if they have a Cho and Darius on their team, what should my team do?

We typically ban Lee, Jax, Wukong, Darius, Singed in no particular order and hope the other team bans some from the list as well, but some slip through.

Renekton late game can 1v1 darius pretty hard. Late game build i have van dam's mercs if they have a lot of slows and stuns, or just ninja tabi, then get frozen mallet, atmas, overlords bloodmail, and blade of the ruined king. Just try not to feed him early and you should be able to shut him down.

Anything that can kite at a distance. Cho'gath and Jayce come to mind but Jayce is a top ban/pick. Also a gank heavy team. One strategy we used against a Darius pick was ganked him so much he became worth no gold and we almost avoided him in team fights. Almost.

I wouldn't worry about lee as much as singed darius, rumble, jayce, cho, riven

Executes when chained are incredibly strong on this map and leave you fighting a 2v3 before one of your players can react

Tanky sustained AoE champions are also very strong.