The EU will retain its current ability to impose lower fines than the maximum, which I imagine they'll do in most cases where the fine would bankrupt a company unless the behavior is amazingly egregious (e.g. "We refuse to do the barest attempts to comply even after several warnings despite dealing very heavily with Europe and collecting lots of data").

That said, the existing legal precedents won't prevent the imposition of much larger fines when warranted after May 25, given the new law's higher maximums.