I never got far enough to push that into a production system but I suspect it would have, yes.

I can see a periodic compacting phase could be useful in a system like that.

In the DB world there's good research around similar topics. e.g. LeanStore and Umbra -- Umbra in particular does some nice things with variable sized buffers that I believe are expected to help with fragmentation https://db.in.tum.de/~freitag/papers/p29-neumann-cidr20.pdf