Not so fast, because I just said I disagree. Here is the Semtech recommended implementation (which, AFAIK, is what TTN and Chirpstack use): it explicitly states that it does not incorporate SF7BW250 and FSK. Which means that it it is simply ‘hardcoded’ to steer to DR5 and is unable to keep your device on DR6.
As to why the ADR algorithm isn’t updated to include these additional datarates: I’m not sure whether that has to do with compatibility, making sure that no device crashes because of physical inability to use DR6/7, or whether that is because it really isn’t welcome. My guess would be the former, and I think DR6 is welcome.