First off I'm newish to openwrt so please keep that in mind as I'm not up will all the nuances between different builds and chipsets. However, I was thinking that while I'm getting 400-600Mbits on wifi6 iperf3 tests I might should look at the little cpu. These tests hammer on the cpu pretty well so I thought that I'd so what I've done for other models and install irqbalance and packet steering. That didn't seem to make any difference so the next on the list was a scaling governor change. It might be possible that the MT7621 chipset is just 880mhz and it doesn't scale. It looks like it should, heck this patch was from 2019 it should have been merged by now if it worked.
https://patchwork.kernel.org/project/linux-mips/patch/20190709182018.23193-3-gch981213@gmail.com/