CMBB v CMAK

[McIvan]

In English the backbone means the hard part. Not necessarily the most numerous part. The hard part of the Soviet tank force were the T-34 and KV-1's. They were, as you have pointed out, at times, not the most

For me the word backbone would normally refer to the most numerous type.

Which is not to say I'm exclusively right, just that there is more than one view of what the word means in English. Actually I've never heard (or at least I don't recall) the word used as you use it.