The "official" way is to use a janky installer with a tonne of parameters and no real way to tell if you've got all the files until you try to install. With an ISO, at least you're starting from a known good base when you repackage things.
I don't think Visual Studio has ever been an MSI, by the way.
There are good reasons for it. I hope a sysadmin isn't afraid of some parameters. We've been waiting a very long time for a minimal/piecewise install capable Visual Studio.
Yeah, no fear here, except none of those parameters set any kind of logging and there's no way to tell if the download completed successfully (yay Australian Internet)
I don't think Visual Studio has ever been an MSI, by the way.