"Fang Yuan had 500 years of experience" is an invalid debunk in methodology
In methodology, the feats are evaluated non-diegetically, so the narrative content is irrelevant.
This is why an argument like "Ayanokouji came up with XYZ strategy when he was 0.00001 years old" (just a made up example) is an invalid argument for his methodological scale because narratively being young does not make his methodology superior, even if it does imply that narratively (story-wise) he is smarter.
Same applies to Fang Yuan. I've seen several people who claim to be methodology scalers scale Fang Yuan to low tier (enmity? ragebait? bias?) because his hundreds of years of experience forged his outsmarting capability, even though his narrative experience is irrelevant to the explicit methods being evaluated. Whether he's 500, 100, 1, or 0.00001 years old, do you really think you are evaluating methodologically if sliding the age-number up or down narratively decides the scale of the character's feats completely?
Maybe the argument is valid in normal scaling if you're scaling by raw IQ and intellectual talent (or maybe it isn't valid because there are arguments for Fang Yuan being the most intellectually gifted in his verse and also scaling by outsmarting capability makes more sense than just raw IQ), but in strict methodology scaling, the debunk that he's old and therefore it's normal for him to be wise and therefore he scales low holds 0 validity as a debunk. Age is irrelevant, otherwise you could say something like Jin Huang no diffs Akiyama because Akiyama is a grown man and Jin Huang controlled macrocosms at the age of 2.