Ocean master is far from glass canon, he is Atlantans that means he has super durability which allows him to survive blows from class 100 characters. His magical lightening took down superman and Wonder Woman but Aquaman tanked it.
If that's your explanation of how cheetah was of able to hit flash then that makes her PIS showing even less credible. Characters were nerfed to make cheetah credible threat.
It doesn't matter what came first, what really matters is consistency, cheetah being taken down by street level characters is far more common then her being as fast flash.