As long as the protocol is purely handled in SW, it’s CPU and nothing but the CPU.
AX Lite (using ARM32 IPQ-5010, quite a bit beefier then MT7621A) in that same test setup as above using PC for iperf testing (see here):
TCP: 195 Mbps down, 211Mbps up.
UDP: 405 Mbps down, 400 Mbps up
RB5009 was at that moment still picking its nose waiting for something to do 
BTW Larsa, as you know I also tested zerotier on that same AX Lite and wireguard runs circles around zerotier as far as performance is concerned on the same platform.
You need to compare apples with apples.
Use a decent CPU and your bottleneck will almost always become your internet connection at which point the whole HW offloading discussion becomes useless.