For us excluding vocals it is typically 4-6. But that's because we favor open "airy" mixes that sound like something a small band could play live in a club, etc. I've mixed projects with many more tracks but, perhaps counter-intuitively, I find it more of a challenge to get a "big" sound with a "small" number of tracks.

No value judgements here....just our preferences. And I should mentioned that often one RT track in our mixes will be comped from many regenerations of that same track...but I count it as one smile

Bud