Due to bouncing through CPU gigabit port lan/wan in+out < 1000Mbps, each wifi is other connector to CPU and should be able to reach half of spec speed (1 antenna 433 or 72)
Try this:
Somehow flow offload has problems with DSA-s hidden vlans too
Feel free to share reports like ones without revealing your IP
Like Sock - link
19 - link
23 - link
23 with mtu fix - link
23 with device exempts - link