Andrew,
Unlike you, I have had issues with the Update Assistant, almost all of which are attributable to a spotty internet connection. I have had several occasions where the download of "all the bits" was virtually complete, had a connection drop, and had to start all over again. I have nothing against the Update Assistant if you have a fast and stable connection, it's just not my preference.
I also like to have an ISO on hand (even if it happens to be an older one for a given Windows 10 Version) in case I need to do a repair install or for doing feature updates on my other machines without the need to download again, which has always occurred with the Update Assistant.
Since most of the time associated with Windows 10 feature Updates is associated with downloading the components that are, in essence, the ISO I'd rather just use the MCT to fetch the ISO so that I know I've got "the whole package" that can accomplish the necessary actions already present, and that can do so whether or not I have any internet connection at the time I'm doing them.
It's really a matter of personal preference, with my reasons explained above.