I think people have covered most of it. Trying to tie it all together in detail:
16/17, Poch’s third season, was our peak. We finished second on 86 points, and in the second half of the season actually got 47 points (which would equal 94 points across a whole season). We were undefeated at WHL. We were on fire. We just needed a little boost to take us over the line. Instead:
17/18
- Had to move to Wembley
- Sold Walker and replaced him with Aurier
- Permanently lost Wanyama and still haven’t replaced him
> Went backwards 1 position and 9 points
18/19
- Unexpectedly had almost another entire season at Wembley
- Also lost Dembele
- Bought NO-ONE
> Went backwards another position and another 6 points
19/20
- Bought Ndombele, Lo Celso and Sessegnon, but all had injury and fitness issues
- Initially didn’t sell or give new contracts to Eriksen, Rose, Aurier, Toby or Jan (all of whom we know for sure wanted to leave and/or were in the last year of their contract)
- Had lost and performed badly in the CL final, after an incredible and emotional run to get there
So I think a combination of our squad getting worse, our manager and squad having been together for a long time, three years of backward momentum, and having come so close but just missing out on PL title and CL (and to some extent domestic cups) - it all finally coalesced this season, and now we’re still in the depressive funk of the hangover.
I think it is 100% crystal clear that the stadium build is the root cause of all of this. What I don’t know is whether it’s close to 100% to blame, or whether Levy and co could have done anything differently in the financial circumstances e.g. successfully replaced Wanyama and/or Dembele in summer of 18/19. Will probably never know for sure. (And to be clear I’m not saying the stadium was a bad decision at the time - just that in hindsight it might actually have been counterproductive!)
For comparison, Liverpool finished 8th, 4th and 4th in Klopp’s first three seasons. Then in contrast to us they spent big on Van Dijk, Alisson and Fabinho, and that was the spark they needed to be CL and PL winners by two years later. Actually makes me feel quite depressed.