I actually believe that Jiggs and Fox is a slightly better MU for Doc, but I don't know too much about Luigi so correct me if wrong.
Mid tiers goes like this for me
Samus/Doc
Luigi
Pikachu
Mario
Ganon
For Jiggs, Doc is a pretty good character, but Luigi both has a much easier time killing her with his very fast and pretty strong moves, and Jiggs has a harder time being lame against him. Luigi can always just nair a jiggs at like 70% and it'll die, alongside actually being able to combo her at low and low-mid percents.
For Fox, I think Doc has a better neutral game, but Luigi has a much better combo game, able to 0->edgeguard[death] him pretty easily. Alongside this, however, I think it's easier for Fox to be lame against Luigi than Doc. I figured it's pretty much comparable.
Sub-high tiers is this for me:
Borderline: C. Falcon
Viable Tier: Samus/Luigi , Doc
Niche Tier: Pikachu, Mario/Young Link/Ganon, Yoshi