Is this because of vulnerabilities baked in the HW (or bootROM or any other unpatchable area)? What’s the situation on older Pixels? Are they generally safer than an iPhone for HW issues? It’s expected that given a few years some vulnerabilities will crop up for most hardware.

So then the best chance for security is to stay up to date with everything, including the latest HW model. At least this gives an attacker a window of only ~1 year to find and exploit a vulnerability.