Devil_Hex
Actually if we need to make fujin op all he needs to do learn flying thunder god technique and use it's seal on his own body ( the seal I am talking about is the one that Minato used to transfer away the tail beast bomb) that way anything that comes into contact with him he can transfer away and on top of it if can keep wind domain ( I don't need to tell you) . But for that he needs loads of Chakra so he can steal Ryuumyaku cave and he can take stone of gelel for physical regeneration. With this alone he will be quiet op . Another thing that goes with it is we know we can keep two m. Sharingan in one's eye socket to give ems so what happens when we keep sharingan and byakugun together there is a possibility he can both those abilities together so it will be easier for him fight close quarter combat.
To increase the speed is very simple, just decrease the friction of the air that is inside the dome. I even believe Fujin can do it without the dome. And adding to the jutsu, I think it would be better for Fujin to split it into two modes: a passive form that would imperceptibly influence the winds around him, so Fujin could have a natural sensor that would put his perception on another level, and the active one would be the dome that was shown.
Minato took 3 years to create rasengan. Fujin creating that wind domain, which seems way more complex than the rasengan, in a little more than a year is just bs. This jutsu has the potential to become fujins trademark jutsu, just like the flying thunder god for minato or the raikage lightning coat. TFTC
Wind Domain sounds great but has a clear downside, namely if the opponent uses his chakra to disrupt Fujin's chakra, this is like Domain vs Domain in JJK, but if the Jinchuuriki releases a chakra burst then it is certain that the Wind Domain will spread, even any ninja who has a large chakra pool and ready to waste his chakra to counter this move