>How many years of secure operation?

I don't believe this is a way of validating the security of a blockchain. Consider the turkey problem as stated in "THE BLACK SWAN" by Nassim Nicholas Taleb: "A Turkey is fed for 1000 days by a butcher. Every day confirms to the turkey (and the turkey's economics department, and its risk management department and its analytics department ...) that in fact the butcher loves turkeys. Every day brings more confidence to the statement. Until one day the Turkey is ripe for Thanks Giving".

You may very well be correct but I don't think length of time without a fatal error is a valid metric.

For me personally, I am in the Bitcoin proof-of-stake camp however I would be lying if I didn't say I also have a position in Ethereum.