> I don't think it's terribly controversial that collaborating in person is much, much easier.
It's fairly controversial, especially among engineers. Not all engineers, but a sizable percentage of engineers are not comfortable in social collaboration - especially forced social collaboration stretching over multiple hours for difficult tasks.
As far as 'easier' goes, 'easier' isn't always 'better'. While that online collaboration across a slack channel may have higher friction, it would also have many benefits as well. Other people can follow the entire process, so continuous status updates aren't required. The chat can be stored so if the issue happens again, it's easy to reference back to what was done.
> But it's entirely unsurprising to me that innovation is more likely to come from collocated teams.
I don't think this is proven anywhere, and may be one of those things where you think it is correct, but it really isn't. Fully integrated remote work as we have today is a very new phenomenon and there hasn't been much research into it. Further, many quick growing startups that are looking very promising are taking the 'remote first' approach and seem to be benefiting from it from an outsider's perspective.