I didn't say anything about disabling OFDM rates, which as you note is not the way it's done. I vaguely recall reading in some of the many
802.11n revisions, there was a clause that REQUIRED dropping 802.11 and 802.11b (non-OFDM rates) if 802.11n was enabled. You could have the slow 802.11 and 802.11b speeds with the OFDM 802.11g rates, but not with 802.11n. Apparently, that got dropped somewhere along the line and I didn't notice. However, for maximum speeds, it's still commonly recommended that your turn off 802.11 and 802.11b: