Wireguard at 200 Mbps does seem too high for MT7621. Wireguard on an ER-X (MT7621) at 160 Mbps mean is reported here.
Not sure what you mean by qca9563 being faster than the MT7621 though. The qca9563 is single core 775 MHz MIPS. The MT7621 is dual core 880 MHz MIPS. Wireguard also can make use of multiple cores. I'd be quite surprised if a qca9563 was faster.
FWIW, I found my ER-X to be speedier than an Archer C7 for SQM - don't recall specifics, but the ER-X was definitely an upgrade.
My experience being my ER-X was faster than my C7, this piqued my curiosity.
The 1004K MT7621 is indeed slower per MHz at 1.6 DMIPS/MHz and 3.05 Coremarks/MHz than the 74K qca9563 at 1.93 DMIPS/MHz and 3.48 Coremarks/MHz (ref: https://www.mips.com/products/classic/).
However, the MT7621 looks like it makes up the Coremarks performance difference per core with its higher clock rate (~14% higher clock rate, ~14% lower Coremarks/MHz), plus it adds an extra core.
Tests done at 28 dBm transmit power. I'm doing ordinary ookla speedtests since I have 1gig FTTH and the server I've been using can easily reach 940/280 (full bandwidth)
Output of iw dev wlp3s0 link command:
Same test, done at 20 dBm transmit power.
Hardware used is Thinkpad X220 with AX200 wireless card.
No walls:
Speedtest by Ookla
Server: EOLO - Milan (id = 11427)
ISP: Dimensione Srl
Latency: 8.85 ms (0.47 ms jitter)
Download: 649.96 Mbps (data used: 694.9 MB )
Upload: 276.84 Mbps (data used: 324.6 MB )
Packet Loss: 0.0%
1 wall: (got better results this time)
Speedtest by Ookla
Server: EOLO - Milan (id = 11427)
ISP: Dimensione Srl
Latency: 9.23 ms (0.14 ms jitter)
Download: 610.30 Mbps (data used: 579.4 MB )
Upload: 277.79 Mbps (data used: 225.2 MB )
Packet Loss: 0.0%
3 walls: (almost lost signal)
Speedtest by Ookla
Server: EOLO - Milan (id = 11427)
ISP: Dimensione Srl
Latency: 9.44 ms (0.47 ms jitter)
Download: 88.80 Mbps (data used: 107.2 MB )
Upload: 64.49 Mbps (data used: 110.7 MB )
Packet Loss: 0.0%
In the end, I might as well consider to lower the transmit power a tiny bit, since I have other equipment in the house that help me cover it all (another wireless router in AP mode with fast roaming).