The focus mechanism on most of the Zeiss lenses is very tough, not so easy to turn - yes it is smooth.
Not so on the Otus, they are much lighter and quicker to focus. It's a day/night difference, who tried it knows what I'm talking about.
You may say you get what you pay for
Is there a chance the Milvus lenses "loosen up" over time?
I understand that with a Macro lense like the 100mm a tight focus mechanism may be of benefit. I use it for portrait though, and when trying with the Milvus 85 I found that one is even tougher. Also the older ZF/ZE lenses have the same "problem"/feature.
Another thing is the focus confirmation beep on the Canon is not always showing. Is this because the high amount of CA from the 100mm lense is giving the confirmation a hard time? Digloyd mentioned that focus on the 100mm can be difficult because of CA, I did not quite understand.