No it is better to have 7 10-plane stacks than one 70-plane stack. For interceptors, I think the optimum number is actually 5, but not sure about this. I sometimes use 6 or even 7 in a stack, but 10 interceptors will take a big drop in their damage due to the SBDE thing.
Gathering up so many low-cost units and walking around the map is about the stupidest strategy you can come up against. It is very easily countered and you can destroy these huge stacks taking much lower losses if you plan ahead, use fortifications wisely and think about exactly what units you would be best off recruiting to counter each particular stack. In practice, you can usually play it so that you end up losing mostly militia, which are a very low cost unit, while destroying your opponent's AT and artillery units.
I started another thread about what I like to call 'fortress complexes' on another thread, and I have been able to use these to great effect against enemies who use this kind of strategy. Of course, if you try the standard mobile WW2 type warfare against these stacks, you will end up losing large numbers of very valuable units (like tac bombers, which will take huge losses against a large stack that is sexed up with a lot of AA guns). So the trick is to use the old-fashioned First World War tactic, and these work very well against what I like to think of as an old-fashioned First World War offensive strategy (i.e. massed artillery supporting a massive assault).