Originally posted by Nephthys
Awful explanations all around. None of that is as much of a factor as his aging, which was already affecting him at 700, let alone when he neared 900 and was a mere 2 decades from dying of old age. It's also all speculative. Yoda says that after 700 he can only lift 5 stones. It doesn't say he can only do that when not trying that hard. Suggesting that he'd suddenly get dozens of times stronger just because he wants to harder is ludicrous. Likewise confronting his darkside and having more practise would lead to minor increases, not the insane one we're talking about.
Confronting his Dark Side made him so markedly stronger that he could transcend death and become a Force Ghost, and so much stronger that Sidious was shocked at his strength and actually feared him...
Not to mention:
Originally posted by Selenial
If y'all want to play retcon games though, The Jedi Path was retconned by the fact Dooku casually lifted over fourty tonnes of similar stones, and Yoda is confirmed his superior 🙂
Which is not guesswork at all, keep trying though.