I think you make some very valid points.
The only evidence we have in how the manager is performing in his role is by what we see on the pitch and the results that go with that.
And of course that is where everything is falling down at present. And then the situation becomes no different to that of Frank at Spurs and Dyche at Forest. Neither of those guys became embroiled in public rants against their employees. But their tactics and results led them to being sacked, with the owners of those clubs deciding that things were unlikely to improve with them still at the helm. Glasner of course does have some ' collateral ' after our two trophy wins. But his conduct has become increasingly unacceptable. And while you are right, we don't know how he behaves '' at work '' , his behaviour with a microphone in front of him is there for us all to see and hear.
I've said on here many times that I supported the decision to let him see his contract out. I've also said that I don't hold him solely responsible for our current plight. But we all know how these things usually play out and that's with the manager being sacked - and that's without Glasners outbursts. Cue the players saying '' we have to take responsibility, we have to take a good look at ourselves '' etc etc.
So why hasn't Glasner been sacked by now ? On the face of it the justification for keeping him in the job has decreased in the last two weeks. I would think that if we fail to beat Wolves tomorrow then his situation becomes untenable. But I can only assume that Parish is either unable to get his man at the moment and is gambling on playing the waiting game, or an obvious, available contender such as Thomas Frank doesn't feel ready to take on the challenge or is reluctant to take over in the present circumstances.
And as you point out, there is no such thing as a guaranteed new manager bounce.
It's interesting to look at other clubs who changed their manager. Forest (or the owner, at least) seemed to grow bored and frustrated with Nuno's ultra conservative approach, coming to see it as an impediment to reaching the big time rather than the reason it was in sight at all. They then went to Postecoglou, who has the total opposite approach. Results didn't improve. Then back to defensive pragmatism with Dyche. Results didn't improve. All these changes, including very different tactical beliefs, and its all made no difference. All it has done is undermine stability, and surely made the forest job a far less attractive one to top coaches than it could have been.
The same could be said of spurs. They flip flop from one style of management to the polar opposite only to find that, when on a losing run, a Thomas Frank team has a very different way of looking awful to a Postecoglou one. It might be that the lesson is just how little difference the guy in the dugout makes if you don't have at least a couple of top players playing brilliantly most weeks, especially in attack.
Of course, new manager bounce can happen, although sometimes I wonder if it's more a case of old manager rebound. United look a different proposition entirely now, but I wonder if that's more to do with Amorin going than Carrick arriving. A similar thing happened when Mourinho went.
Didn't really happen for West Ham, Forest, or Wolves this season when they made a change, though. I wonder if that's on Parish's mind. Leeds stuck with their guy and seem to have benefited, if only from not rolling the dice whilst others around them have. It would be interesting to see if Burnley feel the same. Parker got them up once, perhaps they are already looking to him to do it again next year and that's why he is still in post. The current Bayern Munich manager, who has them flying, couldn't keep Burnley up, so why should Parker not doing so be seen as an unacceptable failure? Clubs used to accept these things and stick with managers. Perhaps that's becoming less unusual, especially when the evidence that changing the manager makes a lasting positive difference is so flimsy.
Parish has sacked managers before, though he tends to do it only when he feels he has someone he can trust, lined up to step in. I felt Glasner was arguably guilty of gross misconduct after the Sunderland game, and perhaps risked getting sacked without a pay off. That Parish didn't go that route suggests he didn't think it in the long term interests of the club. Perhaps that's to do with recognising the benefits of stability, the risks of change, and resisting the temptation towards knee jerk, social media mob impatience.
One thing for sure, Glasner not getting sacked is now as much of a story as other guys getting sacked! What a reflection that is on the wider state of affairs.