Size in diffirent Industries

Tech, Media & Telecomm, Healthcare, Aerospace, Defense, Industrials....the list of industries goes on and classifications may vary from bank to bank.

So far as investment banking is concerned, are some industries larger (more deals, more companies) than others? I don't mean 'Which industry is hot right now'. More along the lines of, in general, how big is the industry?

I get the impression that defense is very small, with virtually no bulge brackets or elite boutiques having defense groups, while industrials is extremely big....with every bulge bracket having an industrials group.

All input is appreciated.