You make a valid point.
Also, many people have this ideal of the fairy tale career for top athletes - they make that final basket (Jordan against the Jazz) and leave the court on top.
however, if athletes are willing to trade a bit of their legacy and historical placement (and ego), they can still make a damn good living, and do what they enjoy, for a few years afterwards.
So Ronnie isn't #1 in the world anymore. There's no doubt he's still one of the top 10 bodybuilders on planet earth. He's one of the top 2 or 3 draws, absolutely. He's more of a household name with fans than Cutler. And when he's ON, he can still out-vascular Cutler (who really won the 2006 Dutch GP?).
By competing in 2006, he lost that undefeated veneer. Just like heath did this year. But in the longer run, Ronnie can compete for 4 more years, still be a top 20 bodybuilder the whole time, still make several hundred K a year, and still have fun pushing himself.
I'd say Ronnie should compete as long as he wants - history be damned. Typically, you don't live thru history anyway, so it doesn't matter if kids are debating Ronnie vs. Jay in 2050.