Well, Mina and Zouma have played together twice and imo have been by far our worst CB pairing. They're both too similar and, in a two, that doesn't work. I agree with your sentiment though.
In Silva's defence, the defence looked a lot more solid until the last seconds of the derby. Since then it's like one little thing goes against us and the entire team caves - it's a worry and the issue is we've seen it before with different players and managers now over the course of five years. It's a huge concern and such a weird thing.
I'd get back to our best team now, and I don't see how the arguments for that not being the same set-up of the side that won five out of seven are based on.
I get Walcott dropping out, but what he does add is movement in behind which Lookman unfortunately doesn't bring. He does bring strengths in other areas though and I'd like to see him get a run now.
Pickford
Coleman (Kenny is playing well though so wouldn't be adverse to him staying in) - Keane - Mina - Digne
Lookman - Gana - Gomes - Bernard
Gylfi
Richarlison
That has to be the basis. Whether it's like that shape, or a 4-3-3 (which I'd actually be open to seeing, and is definitely the formation that would get the best out of Davies if he's needed at all, but also I think would help Gylfi 'be more involved'), we have to get back to that.
I like Dom and Tosun. But neither are consistent enough. Richarlison, for me, is wasted out left with how we currently play. He gets isolated and frustrated. Get him closer to goal and get him working in tandem with Gylfi again. Or play a proper fluid front three of him, Lookman/Walcott and Bernard.