Is it?
Hutton is a better right back than Bacuna in my opinion, I think you'd find a lot of people that would agree - Hutton's not brilliant, but his selection over Bacuna is hardly baffling.
Westwood (or Gardner) over Tshibola again is hardly baffling - I'd have expected maybe Tshibola to feature a little more, but he's been very flat for the reserves and if he's training in the same way then you can see why he wouldn't get a game. Westwood is our most mobile midfielder and possibly our best passer of a ball too - he's also got a dreadful mistake in him, Gardner is less mobile but less likely to cost you a goal. Our midfield is terrible, but selection wise you'd expect to see Gardner and/or Westwood regularly based on what we have to select from - I don't see that as baffling.
On Gabby, I'm surprised we're seeing so much of him, we've Ayew and Grealish who can play the same position - there's the ACN thing though so I guess it might be as much to do with that.
I agree with pretty much all of the rest of your post, we're reliant far too much on individual brilliance, and it means we'll struggle for consistency - but in terms of how far we can go as a team that wins without playing well (without a midfield) - then I think the selections have been pretty good and pretty much as you'd expect.