So, the reason why you can selfhost is because Google Fonts is a repository of FOSS fonts[0]. Google can't strip away the open licensing to evade GDPR, because you can't actually cancel those licenses. They have no termination provision and allow redistribution, so it would still be possible to selfhost even if Google stripped the license. The courts would view the stripping of Free licensing on free fonts to be a subterfuge, and strike it down. Furthermore, if they did this, it would almost certainly violate SIL Open Font License and GPL+FE[1], as they both have copyleft provisions that forbid restrictive sublicensing and require derivative works to be made under the same license.
If we were talking about Adobe Fonts[2], which exists to license proprietary fonts, then the above wouldn't apply and you might have an argument. However, there is no particular reason why website developers could negotiate a self-hosting license for more money. If it's not a legitimate purpose under GDPR to use Google Fonts to save money on hosting costs, then it's probably not a legitimate purpose to use Adobe Fonts to save money on licensing costs.
The correct way for this to be fixed is not to evade GDPR; it's to get Congress to embrace it. Alternatively, someone in the EU with no ties to America[3] could host their own font service and negotiate licenses for premium font usage... but that's more of an interim solution than a long-term fix.
[0] I will only be talking about "font software" - i.e. the copyrightable aspects of the font files we use to render fonts on a computer. Font designs themselves are subject matter for patents, not copyrights.
[1] GPL with a clause clarifying that embedding the font into a document does not require putting the document under GPL.
[2] I had to stop myself from calling them TypeKit still
[3] The lynch-pin of Schrems II is the fact that Americans can be compelled by US intelligence agencies to collect EU data they have access to, so it needs to be 100% America-free.