Here's a link to SUPER-VILLAIN TEAM-UP 8, Oct 1976, by Englehart and Giffen, that teams up Sub-Mariner with Doctor Doom, that seems to me the most logical of pairings. This is the last issue by Englehart, and Giffen did this issue and issue 13.

https://readcomiconline.to/Comic/Super-Villain-Team-Up/Issue-8?id=100918

https://readcomiconline.to/Comic/Super-Villain-Team-Up/Issue-13?id=100907

An uneven run by multiple writer and artist teams, but a sample of what's possible teaming Sub-Mariner and Doom.

Englehart did a long run with Sub-Mariner in the first 11 issues of THE DEFENDERS in 1972-1973, that I thought were consistently well-written.
https://readcomiconline.to/Comic/The-Defenders-1972/Issue-1?id=54189