Well since everyone else draws comparisons with pCARS... SMS have over 100 employees and 80,000+ WMD members (not all of them actively contributing assets), but it's enough for them to have new builds out every day. Kunos only have a handful of staff. Licensing and laser scanning would have eaten up the majority of their funds. They've been relying on the modding community a lot, so I would have expected them to focus more on the framework as you say.
Who knows... but if you asked me a year or more ago I would have expected a final release by the end of this year (of course with active development continuing). But it's still very much pre-release in terms of features and quality in the context of an overall 'game'. In part the community have done this to themselves, we're more than happy to pay for 'early access' and assume devs will deliver on promises. Whereas if we never heard of a game we wouldn't necessarily know if it was delayed and therefore wouldn't mind.
I'd never call AC arcade. There is some stuff I like about it, but I'll admit the physics do seem a little odd to me at times.... but of course... it's pre-release. So I don't play it much for now and hope it'll be great s**n.