Give it a rest. Considering that, as you say, we all knew what was coming, why does it matter that the announcement for Selles came so soon afterwards?
Wilder has form for doing the exact same thing to Hecky before him, and Warnock has made suggestions that Wilder did the same at Middlesbrough when he got that job. But I guess it's one rule for Wilder, and one rule for the rest eh?
Up to when Covid halted our tilt at the PL (arguably a little before that, but I'm not splitting hairs here), Wilder was an immaculate manager. The best I've ever seen for United. But since then, he's been a shadow of his former self.
We slumped to relegation under him, after he was allowed to make some poor signings for big money, and then he threw toys out of the pram when the Prince refused to give him more (for very good reason). He snaked the job from Hecky, did no better in the Premier League, and then failed to get us promoted back there. You can argue about the record points tally all you want, but when we haven't gotten promotion from it, it's irrelevant. I'd much rather be in Sunderland's shoes right now, having earned far less points but having won at Wembley.
There's zero need to delay announcing our replacement, unless you feel like a spell of mourning is required. In which case, I'd be concerned that you idolise Wilder a little too much.