This is not the Safari/Webkit's teams fault, just far too small a team for such a complex project and Apple, without any competition on iOS and an adverse incentive to make the web a compelling platform was not going to fund it. This is in addition to the fact that Google was paying Apple not only for Safari search engine traffic but Chrome traffic as well.
Outside of the stability issues, the gaps in functionality especially for Web Apps became vast and it was not practical to build a viable Web App on iOS. No Install Prompts, no push, no orientation lock in addition to severe issues with scrolll (which haven't yet been fixed) meant the only way to build a working app was to go native.
The only thing that has changed, is that Apple realizes that competition is coming and they need to build a competitive browser. This is why they are investing now. Headcount and the development of Push Notifications was almost certainly related to this regulatory pressure.
This is a great outcome, and just with what's happened in the last year I'm really hopeful for the future.
That said, still quite a number of critical missing features and fixed are needed before Safari can truly be used as an application platform.