This sounds like a very nice compromise actually. I'm surprised it helped with abuse though, since there's a lot of email providers that are easier to create an account with than gmail.
A big part of handling abuse is to recognize that you cannot win - all you can do is better. And a big part of abuse is just raising the bar of sophistication required to abuse you. We went from "any random script kiddie with a gmail account gets infinite accounts easily" to "now someone has to use a custom email domain" (which is easy for us to just banhammer the domain), which both requires sophistication and money. And it makes the banhammer-swing more on par with the amount of effort they have to put in to evade it - banning the domain means go find another domain and pay another registrar fee.
