I made a trade off, being a FreeBSD person I am one degree removed from a lot of the xnu/iOS team and trust them to do the right thing. Empirically it seems like they quickly ship updates for vulns and support phones for beyond their typical first world lifespan. I also trust Apple to worry about the baseband firmware for the lifespan, whereas that is completely unmaintained on all other handsets especially once you use a custom ROM.