That said, I have some concerns that the OpenWRT AP firmware is not as optimized as the Unifi firmware is for that specific hardware. Mostly for wireless performance, but I also don’t want to hit some weird CPU bottleneck.
It's alright except for some shenanigans with DHCP trying to compete with the router, I fixed that by just disabling DHCP on the AP if I recall correctly.
Speeds are pretty much as advertised on the box, the main thing using wireless is the TV as it has a 100mbit LAN port and it it's always smooth sailing. VLAN-separated SSIDs work great as well.
Have you looked at Mikrotik? They offer a more traditional autonomous OS w/o controllers and both a nice CLI and a powerful GUI tool.