Yeah, “we saw the things that didn’t work” is ambiguous. It could be from a technical perspective, like “our engine doesn’t let you take actions outside of your turn so reactions don’t work”. Or it could be from a design perspective, like “we can’t really constrain the frequency of long rests, so the short rest/long rest balance baked into 5e doesn’t work”.

Reading that Larian quote, I always assumed it was the latter but reading this thread I think it might be the former.