What do you think is the point of diminishing returns when it comes to fat/strength? You see some fat and strong powerlifters but it often seems the fella could be just as strong if he wasn't that fat.
That's a very good question, Skeletor. My only certain answer is "I don't know", but I can speculate a little:
If I recall correctly, Brian Shaw was 450-lb at the 2016 Arnold Pro Strongman.
Meanwhile, Ed Coan weighed in at 240-lb in 1998 when he totaled 2,463 in a sanctioned powerlifting meet.
I would tend to think that extra body weight is hugely correlated with strength, but specifically for Strongman, 15-25% body fat is optimal; over 25% and you lose mobility...under 15% and you put yourself at injury risk.
For static lifts, I think more body weight is a more clear advantage/correlation.
But you ultimately pose a good question that is difficult to answer...
For combat sports, I don't think being over about 230-lb is necessary to be the #1 fighter.
For Strongman, 450-lb Brian Shaw is probably stronger than 350-lb Brian Shaw...but by how much?
You asked when diminishing returns kick in, and that's an excellent question.
IMO, the guy in the OP could probably lose 150-lb of body weight, and still overhead press 420-lb.
What does he even weigh? He must be 400+?
So he's adding 50%+ body weight to get a sub-20% increase in strength, right? Although I'm just guessing.
I bet we could map/chart this, and get an idea.
If we took the totals of all weight classes and charted them, we could determine how much body weight percentage [%] increase resulted in what strength percentage [%] increase, then get a more specific answer.
But IMO, this guy could drop 150-lb and still be powerful AF.