till not wrong in saying MM10 was a main game that directly acknowledged the RMW series as happening.
You're referencing DLC instead of the main game. That's not exactly a direct mainstream game to side game reference. It first requires discussion of the questionable nature of the "Special Stages".
R&F's CD database could have easily been brought up without the pretext of "correcting" my point.
The pretext wasn't correcting your point, but rather establishing the relation to your point. That being that though R10 acknowledges through DLC some of the World games, R9 acknowledges through RnF the whole World series and MegaWorld. Making R10 not the sole acknowledgment of World, but rather further acknowledgment.
Were it not for the context of R9's RnF reference, the CD database loses its implications on the mainstream titles as it would be "just a side game referencing side games." Hence, this indirect web of connections is very important for filling the gaps that R10's DLC on its own leaves. From there, as you say, R7 is notable as well, as it references Rockboard, which in turn references both World1 and World2. Completing the picture.
Why isn't the CD database considered "lol game mechanics" anyway
It's part of the whole plot. What with the intro stage being the Robot Museum.