It's reasonably clear that Apple's main focus for Safari is on memory, power use and performance rather than features so that doesn't in any way disprove that they are investing heavily in it.
You'll probably know better than me but Apple's work on Webkit was presumably worthwhile enough for Google to fork it into Blink (no problem with that but maybe worth acknowledging that fact).
I think it highlights a distinction between Apple's past work and their recent work.
Google forked Blink because for whatever reason they were unsatisfied with the state of Webkit -- nominally because they wanted to take a different approach to multi-process, but there may have been other technological and project direction/pace disagreements. Since then, a number of browsers have switched from Webkit to Blink/Chromium as their engine, and arguably Safari is falling behind on new features and overall quality (weird quirks that require web devs to work around).
Don't disagree on features and some aspects of quality but I think it's a mistake not to recognise that the overall user experience also depends on other factors.
If Apple's focus is on getting better power consumption and memory use (esp on mobile) then that's still investing and arguably that does as much if not more for users and the web than adding more features.
PS Let's not forget that Apple are still standing behind WebKit when Microsoft have given up on their own rendering engine so let's give them some credit for helping to avoid a Chrome only web.
Google has a strategy to destroy other platforms and replace them with Chrome.
It’s hardly obvious that this is best for users in the long run.
I point this out not to say it’s wrong for them to attempt this, but because it makes no sense to use Google’s strategic decisions as evidence of Apple’s intentions or investment.
You'll probably know better than me but Apple's work on Webkit was presumably worthwhile enough for Google to fork it into Blink (no problem with that but maybe worth acknowledging that fact).