The "silly version" is just how ONE draws Tatsumaki all the time, with the hair thats just swirls.
Fubuki is def supposed to be attractive, I just think that may be beyond ONE's abilities lol
There is a chance that this was intended in the ONE version but it really wasn't conveyed well. I think the most that Tatsumaki changes is that her eyes become serious, but the dumb hair remains. It also may be that ONE started doing it after the Murata redraw.
I have my doubts about Fubuki. Fubuki doesn't seem to even have eyelashes, or has some really short ones, while other girls in the series and in Mob have them. I think that she may have been intended to have a girly figure, but her face must have been more androgynous, or at least more serious and less super hot girl. Tatsumaki seems to have even less eyelashes than Fubuki in ONE too. Originally Fubuki didn't show up in a fur coat either I think, she is only ever shown on her black coat. Tatsumaki seems to be dressed in the exact same way in Murata, and taken to the logical end in the anime. Although it is possible that in the ONE version, both sisters wear the same clothes that Tatsumaki wears in the Anime, just that they both are less sexy there.
The thing is, Tatsumaki may be supposed to be the prettier one of them both; of course it may be the other way around, and Tatsumaki will end up jealous of Fubuki's figure. Although after catching up on Mob Psycho 100, I doubt this would ever come up.