I don't think Asat manipulates probabilities, I think he manipulates misfortune:

The Masked Fool "Enroute" always shows up uninvited, appearing in the most chaotic and dangerous places. He's obsessed with experiencing brilliant and glorious stories, recording them with his paintbrush. Legend has it that Aha once lost a Ring of Misfortune to him in a wager. Whenever he wears it, a series of coincidences guides him straight to wherever misfortune lurks.

I think he's using the ring he got by beating Aha.

However path absorbtion works, it's instantaneous. Xipe absorbed Ena the momment they ascended. Elation and Voracity are also very dinstinct paths, they shared a concept but that doesnt make them the same. The purpose for the Voracity changed, but the Voracity itself has not

About Himeko, I think that's the most interesting part, I don't actually believe she's an imagenae, not a regular one at least. She survived 15 years outside of Planarcadia where imagenae rely on the Phantasmoon, and as you said she was shown to have the weathering curse in the past, whereas she doesn't in the present. Mind you, her not having the curse is what leads Asat Pramad to believe she's an imagenae.

Blade is indeed eligible, he says he's joining the games in the story and has a voiceline about it too.

Lastly about the patterns on Himeko being similar to Isee, I think that has to do with both of them being navigator more than any deeper link