You suffer exactly what you criticize. You preach cross discipline, yet make an absurd generalization that people from a single domain are the best at not being in a single domain.

Do you have evidence to back this up? Something more then anecdote?

You cannot know everything about every domain. There are people better than you at everything. The balance between specializing and diversifying depends on so many variables. This isn't something you can make a trite generalization about.

edit: And out of the professions I've experienced, the most widely diversified one is "I don't have the data to tell you."