I stopped letting my iPhone update. I swear every update makes it slower and buggier. My old iPad which was perfectly fast and great at the time is now almost unusable after 4 iOS upgrades. It won't even play Sudoko without constant mini freezes.
People would rather use a functional but insecure tool than a broken secure one. No question. It's hard for devs to understand that for some reason.
I don't think it's the added security, that makes new software slower and less responsive.