I always thought the ISO model was a good idea for illustrating and discussing concepts, and I agree that fewer layers (4/5/6 could be compressed into one, I think) are practical. The trouble started when someone got the bright idea to actually define standards around the model - remember FTAM and all that? I once had a boss, many years ago, who thought that the ISO protocols would replace IP!

It's just a model and useful as such. No one in their right mind would actually build to it.