The U6 can process more streams. 4x4 MiIMO of the U7 Pro only 2x2 at 5GHz.

Do not forget that the U7 Pro has an additional 6ghz radio versus the U6 Pro. And the network throughput of the U7 Pro goes from 1gb to 2.5gb if you have the correct switch etc.

I have one U6 and one U7 at home, no problem with either honestly. At the moment, I have two phones using Wifi 7 technology, the rest of the things connecting to the Wifi network range from Wifi 3 - Wifi 5.

Note that the U6 if Wifi 6 (not 6E), so from future proofing point of view the U7 (Wifi 7) makes more sense in my humble opinion.