Ok I think I should set up a scenario...
A mutinous faction has taken over a outpost on the world Bob. A UN Spacy base there is about 2 miles off from the struggling outpost so nuking is out of the question.
The Base that rebelled has maybe
5 squadron of VF-11
1 squadron VF-17
14 squadron of VF-11 era destroids
Proper support craft and transports for a base of this size
100 or so tanks, attack choppers, and the such...
150-300 grunts
Some reaction weapons
The mission is to put down this uprising, your about on par with the M7 fleet.
You arrive at Bob and give a token warning to end this rebellion. When they refuse you launch a force roughly twice the size of theirs. The VF's engage there counterparts and provide cover to the ground force which moves in and captures the base. A special forces squad takes out the reaction weapons.
Logically you dont see M7 destroids because they fought most battles in space. Also the Battle 7 had better dedicated short range defense systems than the SDF-1 and didnt need the extra "umph" of destroids as much so held them in reserve. The SDF-1 barely survived its encounters with hostiles so it needed them more than 7 which had better luck with the enemy in straight on engagements...