Simplifying tenant to tenant migration with one cmdlet where you don't specify destination site (but rather it gets created if it does not exist) would be much better than to do it via GUI, especially when you do not want to migrate all sites, but you have a lot of them (eg 800 out of 1000).

Being able to move Teams with the Powershell cmdlet worked very effectively to both copy to our tenant and add a prefix to the name to match our naming standards. However for the non-team unified group sites I had to manually copy and rename with Copy Structure since the Copy-Site cmdlet isn't able to create a site collection/group the same way as the gui. Basically, enabling something like Copy Teams for these groups without a Team would be great!

Part of this request should be the automatic creation of a site collection when you migrate multiple site collections using a powershell script if the site collection does not already exist on the destination. This functionality exists in the UI so really the request is just for full parody of functionality.

This is, indeed an important ability, but I believe it would need a specific declaration of intent. It would be way to easy to accidentally create site collections in error if, for example, there was a typo in either the site collection name or the path. So, I would suggest enabling this with a switch on the connect-site command, such as "-CreateOK", which will create the site collection if it doesn't already exist at the path, but still connect to the site if it does.

Note to others with this suggestion: There is also a potential workaround - which is to ensure the SharePoint Online modules are loaded, and use the SPO powershell command New-SPOSite before executing the connect command.
Having the option in the ShareGate command would be simpler, though.

IMHO this is mandatory for the powershell to be useful at all.

Whats the point of automation if i have to create all the sitecollections manually before?

The fact that this isn't implemented tells me that the developers aren't really working "in the field" because the ability to schedule a migration to run nightly should be among the first option there is, and without this ability I'm stuck having to click through the GUI at 4 in the morning to make sure it's done by the time our users start working at 9??

Being able to copy site collections in an empty environment with a powershell script (right now we can only merge with existing site collections)