Formations are not written in the stone, in the sense that a manager can be creative within the broad framework of a certain formation. That’s why not all 4-3-3s / 4-2-3-1s / 3-5-2s / 3-4-2-1s etc look the exact same on the pitch. This is not a free rein to improvise at the expense of violating some basics though, because those aforementioned frameworks exist for a reason. They’re time-tested.
Usually, a 3 at the back formation is slightly more conservative than a back 4. Especially for a manager like Ange who actually treats the latter like a back 2 in practice. You have to deal with the fact that it will turn into a back 5 at times, putting you on the backfoot. In particular, if you’re going with a 3-4-2-1 like Ange tried to do, you have to accept that you can’t press that aggressively because you don’t have your usual 3 man midfield. Otherwise, with wingbacks high up the pitch as well, they’ll just play through your 2 CMs. Just some trade-offs that are inherent in this formation, which Ange should have been prepared for.
Instead, he came up with this ridiculous idea of using Gray as a weird hybrid of RCB and DM, leaving him in no man’s land. With Porro pushing forward as part of his role, this left the entire right side of the pitch to be covered by Dragusin. A defender whose Achilles heel is his lack of pace. I know “naive” is one of the most fitting adjectives to describe Ange in general, but this takes the cake.
Looks like he watched a tutorial on YT about how to play a back 3 couple of hours before the match, and just said “Why not?”. Unbelievable stuff.