It takes a while to tx 100+ gb, sure, but you do it once when you get the phone and after that you just move diffs.
It’s not perfect - I get errors from time to time saying music I have isn’t available in my region. Fix is a resync of those songs that got lost.
This is one of those go with the flow situations… the cost is dealing with iTunes, the benefit is carrying around all the music you’ve collected over the years in your pocket.
There may be some non iTunes methods that work as well, I’ve never looked into it.