Thanos is certainly the biggest threat in the marvel mythos from any living villain ( as appose to say a cosmic abstract like oblivion)
I've never suggested anything else, indeed several times early on in my points I stressed the earth based nature of the threats being discussed
But your point about how they view each other isn't that important, this isn't about them and some rivalry or who has the most personal power
The question was who's the bigger threat to the marvel universe
Can you point out a time when Magneto has acted on that scale, on a universal scale or genuine potential thereof, coz dooms got a couple of fair showings
Does doom see Magneto as a potential threat sure, that certainly goes both ways as the scans suggest, but that's not what we were asked