It may vary by your devices
I got a hAP ac2 that has switch chip (required maybe?)
This is workaround for my IPv6 only network, /64 block from ISP

The concept is using a physical ethernet port to assign an IPv6 prefix
- ROS 6 only, ROS 7 is even slower for me
- no default config, no firewall
- eth1 WAN pppoe to ISP
- eth2 assign an IPv6 prefix (NOT a bridge interface)
- eth3-5 as a members of bridge (HW offload by default)
- connect ethernet cable eth2 to eth3

With this setup i got around 920Mbps for IPv6 by nPerf (single connection)
Only have 2 free ports eth4-5, you can add wlan1-2 to a bridge if you want

I tried assign an IPv6 to a bridge got 800Mbps for few hours then drop to 600Mbps
Comments are welcome

That look promising. I've tried something similar on L009 but saw no improvement.
Can you please share your config?

I tried assign an IPv6 to a bridge got 800Mbps for few hours then drop to 600Mbps
Comments are welcome

I suspect that is related to the architecture.. Take a look at the block-diagram and how the ports are shared with each other.

I suspect if you use port5 instead of port4 for example, the speeds will drop again.