But I think you're under-estimating the value of just being a really good version of something that already exists. There was a potential path where Zed would've been more or less something like VSCode, but actually open source, with less jank, with a smaller footprint and better performance, with excellent out-of-the-box support for a selection of programming languages without needing extensions. That, to me, would have been revolutionary, not because it would've had a list of features that's larger than other offerings, but because it would've done everything better than existing software.
Besides, it's not like "AI" is some new thing that nobody has done before. Every single new text editor that's coming out seems to be selling itself as "AI-powered". Zed is now a follower in that crowded space.
E.g. editors often integrate a terminal and file manager. I already have them open constantly, so have never used the integrated versions.
I suspect a preference here has more to do with how many monitors one has. I have multiple so prefer multiple windows. If away from my desk, having a fullscreen window split makes sense.