The big change Vowles brought is focusing on long-term targets and being willing to sacrifice performance in the short-term to achieve them. He's kept repeating that from day one. We won't see if his approach pays off until 2026 at the earliest.

“It isn’t about one year anymore, and for that matter it’s not about 2024 either or 2025, and that’s not meaning to sound defeatist, that’s more presenting to everyone that we have aspirations to keep moving up the grid. We’re prepared to sacrifice the current years to be able to do that.
“That’s a large philosophy change and it’s a hard philosophy change, but it’s one that I’m confident is the right one. We’re not here to fight for seventh or eighth, or for that matter fifth, we’re here to start fighting for proper positions.
“If we’re going to do that, we have to accept that we’re going to break infrastructure, break systems, redevelop ourselves, not leave any stone unturned. That’s difficult for organisations but that’s the path we’re on.”

Williams ended up where they are by only living in the here and now and neglecting the long-term. They always put everything into the car to maximise short-term performance and did not — to be fair, for many years did not have the means to — invest into and evolve their infrastructure and procedures for the long-term. You do not recover from decades of underinvestment and failing to evolve with the times by only doing small incremental changes that don't break anything. Doubly under the limitations of the budget cap.
Vowles last year talked about how 2024 might see them go backwards in performance:

“I’m more focused on making sure that we make a good step next year.
“Now, the good step’s an interesting one, because even in those terms, we may not step significantly forward in performance.
“But what I’ll see is structured systems in place rather than our methodologies, and for most of that it means I’m going have to break a few things. To break it may mean you go backwards in the short-term, for long-term gains.

Considering the scope of the changes they made over the winter, the 2024 season actually didn't start too badly. I was fearing another 2018 or 2019 disaster. Vowles pushed the team to the point of breaking but luckily did not ignore their limitations and aim for something they are in no position to pull off like Williams did under Lowe in 2018.
The FW46 started on the back foot and is falling behind on development, but it doesn't appear to be fundamentally flawed. We'll get a better idea of its potential when the first significant upgrades arrive, hopefully starting in Imola.