Migrating from Google Drive to iCloud Drive

Hi... presently, I sync a large font library and vector graphic assets between 2 mac machines (iMac and MBP), using Google Drive (just too unstable to be dependable)... and am now in the process of migrating to iCloud Drive... (I have copied about 30GB from Google Drive to iCloud Drive (which itself, took all day) (purchased 200 GB iCloud plan)

I understand from previous comments that the initial upload to the iCloud server is painfully slow, days if not longer... if that is the way it is, fine... but was wondering why (technically, or business model) that is so...

For a month or so, I plan to keep both Google and iCloud, but would love to get rid of Google Drive... so, I just wanted to ask what the general user experience of iCloud has been for those that need to sync between machines...

Thanks