Skia relies heavily on runtime shader compilation, which is slow and causes frame jank but improves peak performance. Skia also supports much older devices than Flutter does.

There’s no free lunch, Impeller has a different set of trade offs that are a better fit for Flutter.

It's the old coupling versus cohesion problem, isn't it? The tighter the coupling the more likely that abstractions leak across API boundaries. The tighter the monorepo the less likely there's a concerted effort to avoid breaking changes and consider long term API stability.