I guess they don't want to make Rampage seem like a B-show, otherwise I think they would've just put one of the Dark shows on TBS.
Turner probably wants a flagship show on both TBS and TNT, like they want Dynamite's audience specifically to also watch TBS, but have something for them on TNT.
So I imagine Rampage is going to be treated as a big deal. Considering it's going to come on after Smackdown, it's gonna kinda have to be. Because as Raw is a testament to, 3 hours of wrestling on a weeknight can be a chore to watch.
But then again, Raw is trash, and SD would be trash if it did not have the luxury of being carried by the Roman storyline, so if AEW could come with an entertaining block of programming after that, it might not be so bad for the viewers.
Rampage shouldn't be something that drags, or has a bunch of jobber matches, or highlights, otherwise it probably won't do Dynamite numbers.
I don't know how often Impact has Saturday night PPVs, but I think AEW should've tried maybe a Saturday night show, tho.