This seems all a bit self-inflected. What is it that makes Squarespace so untrustworthy? I've never used them...
The way the dns was set up for my businesses and dn.ca was all the dns, including main address, subdomains, forwarders, mx(mail) records etc were controlled by google domains. When the changeover happens that would all have fallen to squarspace. Squarespace is much like wix and similar companies and there is no way I can trust all my dns, mail delevery etc to a commercial entity whose sole purpose is to sell more services. One day you wake up and something won't work.
Now most of my dns is self managed at whc and I have total control. Over at squarespace I have no idea how it will be run, or what the control panel will look like. I cannot chance giving control of my sites to a company I know nothing about. Plus a .ca is $30 USD per year as opposed to $10.99 CAD at WHC.
I am in a group of other coders, every single one of them is moving out of google domains for the same reasons.
So the rush to get this done is that I am totally familiar with the google domain setup and control panel and with google I was also able to flush my dns records worldwide to refresh to whc. So getting out with a familiar control panel before things switched was key for me. A lot of this functionality will go away or be controlled by a wix like company after the changeover.
Have you ever tried to move data out of wix? It's almost impossible, if you use their forum software you are locked in forever and cannot move the database out. There is no way you can truly trust companies like that when you are running a serious business on them.
PS. If you look at my pic above, they are already making changes at Google Domains and I had my first errors ever there. That has never happened and is probably a sign of things to come with this massive changeover. For me all is safe now and in my control.