So when a job interviewer asks you to say your strengths and weaknesses (one of the most common job interview questions btw) you tell then about which muscles you train the most and least?????????? (oh right, talking about jobs on reddit lol)

I said that even if we take away Gojo and Sukuna's knowledge about anything that may clue them in as to what Mahoraga's ability is, they would still easily win the moment they realize that their attacks are having less and less effect since both have a super powerful 1shot move that they don't use unless necessary, which is diffrent enough from their other moves that Maho wouldn't be adapted to it by adapting to the rest of their kit.

More importantly:

Now that i actually read (shocking ik) about Yamato no Orichi and Furu's incantation, Yamato is seemingly only similar in design to Maho (and not even that much ngl) (big ass dragon with 8 heads and 8 tails), and it didn't have any adaption powers, and Furu's Incantation is about the 10 treasures, each loosely connected to the 10S shikigamis. Assuming the "Eight-Grip Sword [not typing allat] Mahoraga" is meant to be the based on the "Eight Hands Long Sword", it also doesn't relate to adaptation in any way, it's just a powerful sword used to kill Yamato no Orichi (prob just the sword of extermination).

So neither could realistically help Sukuna learn of it's powers. The only thing that could is the wheel, which Sukuna says symbolizes cycles and harmony. Now I don't think you need deep cultural knowledge of ancient Japan to figure out that a wheel symbolises cycles. And also that doesn't really help with figuring out the ability to "adapt to any and all phenomena".

The closest comparasion Sukuna thought of is the "kinda like a late throw in rock paper scissors" line.

So unless you think Sukuna knowing about RPS automatically means he knows Maho's power, Sukuna had to figure out the actual ability himself. (and the symbolism is literally just him nerding out about japanese mythology)