All of the above indeed!
I expect this would be better shown as a loss per flyinghours equation. Fleet size alone doesn't give the full picture - type, role, generation even all play a part.
You can talk about the loss rate in the '70's or 80's but in the 50's it was frankly mindboggling. There's a thread lurking around on the Meteor stats somewhere, I'm surprised anyone got life insurance.
Somethings really are better these days.