Much? Don't use Apple. It is worse than Android. Google Android is bad as well but you can make substantial changes. Beste would be a custom ROM but that's an extreme change and way
You don't want to change iOS? You have to get rid of many Apple apps but I guess, it's not possible.
I use Huawei Health to sync my Workout Data from my watch to my Phone. I don't really know if i can get rid of it, as its the app my watch works with. (Huawei Watch GT 4)