I want full control over sites and Office 365 group creation and I’ve seen the setting in SharePoint Online Admin for ages to specify my own form URL. My bad for not testing this earlier.
Well, turns out, this does not replace the default form, which still allows me to create an Office 365 group off the, but instead adds a tiny tiny link on that form which no one will ever click.
Seriously? Which leaves the only option left, hide the “Create site” link altogether, and tell users to go to my fab order form instead.