This is a little disingenuous, especially in regards to McLaren. Stella came in in December when Seidl resigned and instantly made some very sweeping changes including switching up the way things worked within engineering departments back at the MTC, the aero department in particular where we now know the heads of the department had been stifled and sidelined by Key. We are staring to see the effect of those changes with the b-spec car (the last thing Key had a hand in was the Baku upgrade to the old car). There's a very interesting in-depth interview out with Zak this week where he opens up as to what was actually going on at McLaren around the time of Seidl departing and Stella coming in and what had been happening at the MTC that led to Key's sidelining and eventual sacking. It explains a lot, not only in regards to why the 2022 car was so flipping mediocre but also gives a large clue as to why they didn't fight harder to keep Andreas Seidl when he wanted to leave. It's worth a read actually - a good illustration of how much a team can shoot themselves in the foot internally by having just one person in the wrong position.
Vowles hasn't been at Williams long enough to make a difference performance-wise at Williams but what he has brought a visible difference to is the culture and spirit within the team and that shouldn't be underestimated. From a people management point of view, at least, he is proving to be exactly what they needed (kind of reminds me of Seidl in that regard when he first took over at McLaren and turned the team culture and spirit around in 2019).
I think the biggest problem at Merc is what I'd call the hangover of success. When a team has been at the top for as long as they have, a certain amount of complacency and to some extent entitlement kicks in. A similar thing happened to McLaren back in the early 2010s and also to Ferrari post-Schumacher. They got used to winning, they expected to win, and to a large extent they felt entitled to win so the road to acceptance of failure and turning that around becomes much tougher because accepting they were wrong is harder to swallow. We saw that very clearly with Merc last year and to an extent the start of this year as well. The two teams who have affected huge turnarounds recently (AM and McLaren) did so because they held their hands up, admitted they had screwed up and chose to take the pain (and accompanying ridicule) of falling down the order for the months needed for them to start over. The willingness to do also came about from new blood being appointed in the team - Szafenauer out and Krack in at AM and Stella taking the helm at McLaren. Not saying at all that Toto needs to go but a shake up at the heads of departments may not be a bad thing. They may not be coming from as far back as AM or McLaren were but they still need to be willing to make some sweeping changes to properly progress imo.
I also think Merc also got used to just being able to chuck as much money as they liked at a problem to sort it out and they're struggling somewhat now they're not able to. It's no coincidence that the two teams struggling the most to turn things around under a cost cap are the two who were used to throwing endless amounts of cash at everything - Mercedes and Ferrari. Yes Red Bull have a lot of money as well but they did always operate under a budget that was significantly lower than Mercedes or Ferrari. I think it's been a big culture shock at Mercedes, not just to Toto but throughout the team, and it's taken them a while to get their heads around it. I'm still not sure they have - sometimes Toto says things that make me feel hopeful and other times I'm not so sure.