Seems to have slipped off dramatically the last 2 or 3 fights and ain’t the same fighter he was. Could be age or could be that he’s finally fighting clean. We’ll never know. He should quit while he’s in my eyes undefeated as at least he can make a claim to being the best MMA fighter ever
His decline is probably combination of everything you alluded too. But, whether he loses or not won't diminish his legacy; that **** happens in UFC. Just about every legendary UFC fighter has a loss. He will go down as an all-time-great . As far as the "GOAT" status with Jones, it's either you love him or hate him. If you do he is the GOAT, if not lying, cheating, sociopath POS. There isn't much gray area with him.
The biggest thing seems to be he is fighting guys that are now the same size, that massive reach advantage he had to keep guys away from him made him look untouchable which he could then do his magic with out worrying too much about getting smashed in the face.
It could be that he is fighting clean. He hasn't looked the same since the second Gustafson fight where he caught a bunch of **** for "Pulsing."