I think it was, but I can't find confirmation anywhere.
It was assumed. The story doesn't make as much sense without that assumption. The Molecule Man contained the power like a battery and Doom was using it until Reed broke that connection.
Doom with all that power can't take down an IG wielding Black Panther or a Phoenix powered Cyclops without effort.
He requested help from Maestro, Goblyn Queen etc, where Thanos was beating down high end cosmics and just willing half of the universe dead.
No telepathy, precognition feats etc.