Is there anything I can do to reduce bufferbloat on a separate AP from my openWRT router>?

Have a go changing the AQL settings for your wireless PHY's? It improved things for me.

But yeah wireless is a shared half duplex medium. You will have contention issues.

Examples below for people using it for gl-mt6000. I've done it on ath9k/ath10k and mt76.

https://openwrt.org/toh/gl.inet/gl-mt6000#adjusting_aql