A.G., I get that. I just don't think there's all that much variety involved in simply hitting every club. Maybe I'm in the minority, but to me there's not that much difference between a full wedge and a full 7 iron. There's also not that much difference between a 5 iron and 3 iron. Now, if I only have to hit clubs PW-7iron on approaches, then I tend to think a course lacks variety. But within that spectrum, it doesn't really matter to me whether I hit all 4 clubs or just 2, as they're all short irons in my view.
What's more significant is if I have to hit different types of shots. I might be the only one left, but I work the ball a lot. If I can hit my stock 5 yard draw for an entire round, I feel completely comfortable even if I have to hit every club in the bag. My ballstriking isn't tested thoroughly until I get called to hit a different shape, or hit one high or low.
Going one step further, approaches from 135, 145, 155, and 165 are all stock shots for me. I'm making the same swing whether hitting the 7 iron 165 or the wedge 135. But when faced with a 160 yard shot, I have to manufacture a shot. I'm much more likely to mess up the choke-down 7 iron or slam 8 iron that I'm facing from that distance.
So yes, using more clubs is an indicator, but if a course is going to provide a thorough test it's more important that I get tested across different SPECTRUMS of clubs (balance between long and short irons) along with different shot demands for those shots. A course on which I hit 9i, 6i, and 3i of all different shapes and levels of "power" is a far better test of ballstriking than a course on which I simply hit PW, 9i, 8i, and 7i, even though I hit more clubs at the latter.