Both are cortex a53, both are dual-core, both are ~1.3 GHz (1.35 GHz in the case of the mt7622bv/ rt3200), so don't expect much of a performance difference in terms of the CPU power (well, the wr3000 will be clocked 50 MHz slower) and both are relying on very well optimized networking drivers and hardware flow-offloading into their packet engines. As moeller0 already implied, their raw CPU power isn't bad, but not stellar either.
When it comes to sqm/cake, most of the offloading flies out of the window (hardware flow-offloading is not compatible with sqm, software flow-offloading technically is, but loses most of its offloading potential (so it does make sense to keep it disabled)), which means you're relying on the raw CPU power of its cortex a53 core - and that is not much of a step forward from the previous generation of routers' (mvebu/ ipq806x) cortex a9/ a15 SOCs. Here the exact details of your internet connection matter, plain DHCP is lighter on the CPU than PPPoE, which -in combination with sqm- will have quite an impact on your throughput.
still applies, x86_64 or the RPi4 (cortex a72) are a major step up, compared to the low-performance cortex 53 SOC.
As for the question of mt7622bv vs mt7981b, if you compare them under identical circumstances (big question, PPPoE yes/no), I would personally expect them to perform similarly (the 50 MHz advantage for the mt7622bv shouldn't be that significant), but driver maturity might still favour the older mt7622bv at this point.
It would be quite interesting to benchmark mt7622bv, mt7981a, mt7981a and mt7986a under identical circumstances.