"Any chance you remember what version of the kernel was reported by uname in previous firmware releases?"
When I updated firmware have not interested in openWRT router firmware. So I did not use ssh.
I would not downgrade firmware, because I use the router.
Older firmwares can be downloaded here:
I'm a beginer in that field, so my next idea may be strange.
The openwrt-19-07-8 relase (OpenWrt 19.07.8 service release) use Linux kernel 4.14.241.
The newest Asus firmware use 4.4.60 kernel. Without kernel building, could we make openwrt-19-07-8 firmware image?
Or simpli we install openwrt by ssh?