Woah...a lot to unpack here. Not going to respond to it all coherently and others have articulated a lot of what I think already but a couple of reflections:
Success is not as binary as has been made out. You have to apply context to every situation, as Jazz and others have explained. We should judge each season on its own merits and within the context it was completed. It's also relative; you should judge it based on where we've come from. Slot winning the league in his first season ignores the context of Liverpool being consistently competitive for a number of years under Klopp (plus...Mo Salah as a generational talent).
Secondly and apologies if this more personal but I think managing your own expectations has to come into this discussion. The trajectory of this season has been telegraphed for some time based on the clear problems we've had up front all season. And that was a failing of the summer window, the way we approached it as a club etc. But if you constantly recalibrate your expectations to 'high' every time there's even a sniff of weakness from our rivals, you're going to end up being more devasted than you need to be and subsequently project our situation as being far more dire than it actually is. Which is why everyone from the Kroenke's down to Arteta, our captain and most of the other players are getting accused of being failures this week. Which I don't believe is accurate or in proportion. The club fucked up this summer but to suggest that everyone involved in this project is a failure is misaligned to reality.