Password API works with third-party password managers. Not perfect, but LastPass works pretty well this way. Security Code autofill is also great for 2FA SMS things.
Device performance/reliability, mostly related to launching the camera, although this probably applies all-round. There's nothing worse than trying to take pictures for a group and your camera app just... won't work.
Feature polish (although limited). There are a lot of features that I wish existed, and features that I wish I had more control over, but the overall polish on a feature's functionality and feel is great.
Airdrop. Supposedly Android has a good competitor coming?
Share Wi-Fi password with contacts.
Sign in with Apple + Auto-hide your email.
:( Shortcuts. This is great, except writing them sucks for anyone even slightly code-proficient. Next to impossible to set up on phones. But again, polished but limited vs Android.
Facetime. I really wish Duo was better integrated into Android and marketed.
I'm sure I'm missing some, and I'm purposely not listing the things I miss from Android. There are other Apple-specific reasons that I've decided to stick with iOS for the time being that are also good to consider.