Distributed Switch Architecture refers to the switch control software. OpenWrt is slowly converting targets from swconfig to DSA.
Even if the R4S were still swconfig, I would still not import a backup from a different device. Any device specific configuration difference, not just DSA, is going to create an annoying bug you'll waste more time finding and fixing then just starting fresh. With DSA its the network file you need to worry about, so sure, use your backup as a guide (firewall rules, dhcp setup, etc.), but I would configure your new device manually.