The Flint 2 GL-MT6000 looks promising for a one router solution, albeit a bit on the expensive side considering your hardware requirements are already met with your current set-up. But if price is no object...
Aside, I don't understand why lack of true DSA support would rule out the DL-WRX36. It's network configuration (i.e., /etc/config/network) is very much like DSA.
However, I wouldn't get a DL-WRX36 to upgrade WiFi performance over an E8450/RT3200 (though it clearly has a better CPU, more memory and 2.5G WAN going for it over the E8450/RT3200). I use a NanoPi R4S with a GS308T switch as my gateway, with dumb AP's on each floor connected to the GS308T with wired Ethernet. FWIW, an RT3200 provides better WiFi throughput and WiFi stability at mid to long range in my environment than a DL-WRX36 I tried that is now stored as a spare in a closet.