On the platform security side, Apple is about 5y ahead of the rest of the industry. Look at iOS specifically, and the secure element/trusted boot/etc. process.

(This isn't a general iOS vs. Android argument; I prefer Android in a lot of ways, just not for security.)

The problem with Apple is they do everything, and with very small teams, and end up with elements of widely varying quality. Their online-services security, to date, has been subpar. They aren't terribly fast with patches for known vulnerabilities. They are exceptionally good at platform security architecture.

(We've also got a really smart security guy from a satellite tv company...the satellite tv crypto/hw security world was >10y ahead of everyone else for a long time.)

Has there been a release of iOS yet for which there hasn't been a root exploit released?

Honest question, just based on the prevalence of "rooting" your device and running non-blessed software.