A part of your second from last paragraph reads like you think not having inverted fullbacks in football is a quirk of Thomas Frank's. I don't remember our club having inverted fullbacks before Postecoglou was manager.Strawman?
Obviously but we're talking about just one more game.
Porro coming in field is fine and it's working, what we lack for deep passing he is providing it, you don't want Porro stuck on the wing in this team when he is arguably the best progressive passer in the side, all well and good saying that you want the full backs to stay wide but you're not going to progress the ball very well...i.e Frank ball.
Pointless changing the system now, it's what it is - this system has allowed us to be even within a chance of surviving and we are winning the xg battle more often than not, it means the issue is down to personnel, not the system.
Personally I don't see how it's any better for Porro to pass the ball forward coming inside, than passing it forward from the wing, If that's not the case then why not just put Porro in the midfield to start with, and play Spence at RB, then we can have Porro's passing from inside, and Spence using the wing.
I know none of this is going to happen and De Zerbi isn't going to risk changing much now, I'm just stating Porro can be Porro in the midfield if that's where we need him.