He said the issue was poor supervision
Hmmmm, it could have been. It could have been that he didn't "like" his supervisor, or that he was unprepared to take his supervisor's advice, or that his supervisor queried hm ... it's a complex relationship & if there are failings, generally (setting aside clear negligence) both parties to it bear some responsibility (albeit in different proportions).
I make this comment because your account of your DH suggests to me that he's quite unrealistic and/or arrogant and/or uncollegial. Anyone who talks about teaching thus:
He had some teaching duties early on in the PhD, but I remember he complained about students not often coming to tutorials is certainly unrealistic. Students often don't turn up, the silly idiots.
Not being at the viva ? Generally, we're only allowed i the room at the candidate's request. And unfortunately, I have sometimes had to be elsewhere during my supervisees vivas - but your DH's supervisor arranged for a bottle of champagne - that is above & beyond !
From what you have said here (and I know it's a partal picture at second-hand) I'd say I doubt your DH is cut out for academia.
And that's OK. It is not a failure to go into industry - many PhDs in STEM and HASS do. It's actually increasingly being spoken about - that something like 80% of the Doctoral students we train do NOT go into academia.
I think your DH has some deep self-reflection to do - he needs to stop transferring his doubts about himself & his career choice onto others = his apparently poorly performing supervisor, the new research team head, the students ...
What he as experienced is a pretty First Class academic journey so far (in terms of a flying metaphor!). He's now realising that the long career of an academic is much more like Premium Economy with occasional upgrades to Business. And being a professor is really not like flying First Class for the rest of your life (oh that it were!) - there are more compromises, a lot more work and responsibility, and a lot of advising people like your DH.