To be honest, many of the first batch you mentioned were a) huge downgrades on their predecessors (Sanchez, Aurier, Sissoko - that they were the replacements for Toby/Verts, Wanyama and Walker is an utter indictment of whomever bought them), and b) mostly useless backups promoted to roles of inordinate influence in the side (Dier, Winks, Davies) by dint of just sticking around here despite being wastes of space and wages.
Dier in particular has always struck me as having a terrible meteorology - this 'Dier is intelligent' stuff ignores the fact that, for five seasons now, all he's done is shoot his gob off to the press every time we' re in a run of good form, and get into fights with fans and act the hard man when he's useless. He can' t defend, has no skill, no heart and no brains - why on Earth is he talking for the side?
The only one that I can genuinely mourn in that lot is Dele - he had the world at his feet and threw it away, entirely by himself.
But I think in general, the awful mentalities built up over time. In 16-17, none of that lot bar Dele got into our first eleven, but Sissoko, Aurier et al crept in in subsequent seasons and ruined the competitiveness of the side as the best players left or declined.
It's on Mourinho too, of course it is - he had Rodon, he had Tanganga, he had academy lads, he could have done a Poch, drummed out these fools and played the kids. His choice to stick with them, and they've killed him. Nobody else to blame.
But I loathe these guys right now. They are also to blame.