Why taxes are proportional to income but fines aren't?
And worst case scenario define revenue in the fine's terms in a way that it disallows accounting tricks.
GDPR is really a "fine whatever they want" regime, starting small and increasing for non compliance.
I think the "whichever is higher" wording does make it a floor but you're right that the "up to" makes it whatever they want. So I guess it's a meaningless variable floor.
It still works out similarly: they could fine a company like Amazon, with a lot of revenue, up to around 21 billion (regardless of profit) while they could only fine a small company up to 20 million.
And it would make sense to be revenue-based, as opposed to profit-based.