No offence intended, but I really don't think you're getting how Rumbles work.
We don't "lowball" thought balloons, comments passed by characters, or narrative comments. We pretty much ignore them completely. They're usually hyperbole, and always designed to add drama or build a story.
The only things that we really acknowledge are what the characters actually DO. Feats. And not feats involving other characters forgetting to use powers or speed that they've historically been presented as having. So if Supes is shown moving at a significant fraction of lightspeed, and Doomsday is keeping up with him, then it would be considered legit. If neither party are practically (i.e. not via narrative) using superspeed in the incident in question, and in this case they weren't, then it's not a speed feat.