How do you make such assessment that no F1 related tech person did?
As far as I know, start of the season is the end of it. They only get one new PU for this year. Not sure if they can delay, and use last year's, that would surely mean dragging around last year's chassis for Ferrari.
I can buy such Honda gains, but I'm doubtful there's much to have for Mercedes. They say it cost a lot of effort to even get where they are. I don't think they suddenly found a good chunk of unexplored potential.
(you added an asterisk, but didn't follow up)
As for Honda, I wonder what will happen with that. Andy Cowell and other rumors have died out. RB stated that they wanted to sort it out last year, but they didn't.
I don't know why they can just convince Honda to remain on a cut back budget, with some additional funding from RB. They'll need to keep something up for IndyCar anyway. Let them focus on MGU if their intention to develop EV tech is honest, RB can hire people (and/or pay for the current ones) to improve the engine.
Not much chance until they're running hybrid engines, I suspect.