I tried flashing to Gargoyle v13 yesterday and it actually was worse performance wise, so I fell back to v12.
what's weird is the CPU doesn't appear to be doing all that much according to the dashboard.
Someone on Reddit r/OpenWRT a few years ago said they did manage to eek out much better performance on a v2 using v19 and Flow Offloading. [Archer c7 v5 on latest image (19.07) slow LAN-WAN]
I have a cheap Netgear WiFi 6 (WAX202) on the way so we'll see how that does.