Mate, no
I get you've formed your opinion on him and nothing i say is going to change that, but on this you're wrong and it seems like youre letting that cloud your judgement on it, if i may be so bold.
It 100% was not the right time to do it. It's completely different to Brands being there for Ancelotti etc - there was no chaos at that point. If you put Thelwell there at that press conference, you shift the attention away from the new manager and make the story all about the utter catastrophic stuff going on at the club. Thelwell AND Kenwright should be fronting up and addressing the public, but in no way shape or form should that have been at the manager's first press conference.
Had circumstances been different, then yes, of course Thelwell should have been there, but had circumstances been different we'd have had a press conference just to introduce the new manager rather than tie it in with the pre-game thing.
The situation is what it is. Thelwell may or may not be incompetent and largely to blame for the last week of this soap opera of a club, I honestly don't know, but that doesn't mean we suddenly throw objectivity out of the window.