The belts need switches in order to function, but it was never said the Meteor belt needed the Meteor switch specifically to work. The Elec and Fire switches only give Ryusei electric and fire attacks rather than actual weapons.
I agree with that, but also think that it's a vessel to make use of the Cosmic Energy, while containing some Cosmic Energy itself. I think the reason for the M-BUS' CE Cannon is that possibly one switch does not have enough Cosmic Energy to power the transformation, while Fourze's four switches have enough CE amongst them to activate his transformation. the Meteor Switch probably also contains the makeup for the Meteor suit, as in the Fourze Driver toy, it's treated as a Rider Switch in the voice used. so if Fourze were to use the Meteor Switch, it would probably create a Meteor Module modeled after Meteor himself, similarly to how the other Rider Switches work in Ganbaride