You are right in most cases the presence of 802.11b degrade the 802.11g.
However the level of degradation varies from few % to 50%.
In needed to connect two computers for Internet purposes only, so 802.11b is good enough.
So happened to be that I had a 900AP+ sitting in the closet and I decide to actually test it. I configured the 900AP+ as a Client plugged it into a Switch and plugged the two remote computers into the Switch.
I left it off and use Qcheck to measure the bandwidth of my regular 801.11g to 802.11g connection.
I switched the 900AP+ and the other computer ON, I measured the 801.11g to 802.11g connection again and the presence of the 900AP+ On but with no real action degraded the 802.11g to 80211g only by 5%.
I then put my grandson on the other computers and told him to Use the Internet.
Measured again the 802.11g to 802.11g bandwidth and it was further reduces but what you would expect by two other computers using the bandwidth.
So I left it as is.
However, each one millage might vary, that is the reason I added in my previous post the general remark about compatibly.
:sun: