Some people will come up with some of the most "interesting" excuses. And I am being nice by saying "interesting".
Some of them include things like what you said, plus:
"That feat occurred 30 years ago, it no longer counts."
Of course, I've used that too and this excuse "does" have at least some merit, but it doesn't work for every character nor for all debates. I've also heard:
"Is the character's feats consistent? They aren't? They don't count."
"This character is not a team buster, he's only done it once. It's an outlier and to be ignored."
"This character has no lifting feats so he is NOT stronger than my favorite character." (Despite the fact, said character has beaten other characters capable of beating his favorite character, with the scans to prove it).
"Does this character do this kind of feat consistently over the course of time? They don't? They don't count." (This excuse makes people justified in claiming Superman cannot fight or does not know how when he CAN fight)
"She demolished that guy!"
"No she didn't, all she did was hold him by the throat."
"Did you read the issue? She BEAT him!"
*Shows Scan that clearly shows otherwise* "No, she didn't. She did not win that fight!"
"SHE DEMOLISHED HIM!"
I can go on and on with the endless excuses but you get the point. So, it sounds like these guys with Orion and Silver Surfer are just trying to make excuses here.
Now, to answer your question: Thanos DEMOLISHES Darkseid in a real fight. No ifs, ands or buts about it.
That is, a fight that is taking place in a sanctioned and actually published comic book (but a movie or tv-show would do just as well I guess), I think the probability they will be portrayed as equals, or close enough to it, is pretty good.