I think people with a long history of obesity do not fully recover from the toll it has taken on their heart-lung system until (and if there is) a long period after great weight loss.
Meatloaf’s stage performances were like a giant physical work out, for an average weight person, which he was not, and the whole time while he had asthma as well. I do believe the late in life weight loss did not ever fully compensate for the prior history, in his case, and that history made him more vulnerable with a Covid19 infection - my guess.
People in the music business are not known for their healthy lifestyles, generally speaking. His health might have been less than optimal not because of excess weight or weight loss, but because of years of too much alcohol, drugs, junk food, lack of sleep, lack of exercise, etc.