I understand the skepticism. However, the crankshaft does
put pressure on the seal. Loosening the bearing caps for even a few millimeters of droop will relieve this additional pressure and make it easier to break the seal loose from the groove and extract it. I tested this back and forth myself when the seal had broken loose, just to make sure what I was experiencing wasn't just in my head. Wanted to be sure I didn't fool myself in to thinking it actually worked like I expected it would, when all I may have done was "loosen the jar lid without realizing it".
After I loosened the caps enough, I was able to finally break the seal free, and with much less force than I was trying before. Thought "Hmm... might be in my head" (along the lines of your suspicions). So I tightened the caps back up to spec - now the seal was in there tight again and only the metal core would budge when I tried to drive the seal. Hmmm... Loosened the caps again and the seal was easily driven again. Loosening the caps had a direct effect on the pressure placed on the seal, and the friction the seal experienced in the groove. It can make a difference in ease of extraction of the old seal.
Is it necessary to loosen the other caps to replace the RMS? Certainly not, or it would be part of standard procedure. But it can make it easier all for the cost of turning a few more bolts. And considering all the freakin bolts on the oil pan, what's a few more bolts?