you do realize that current strange is pitiful compared to classic Strange.... but fundamentally I agree. CK was supposed to be a multiversal threat and Doctor Fate and Strange at their best were universal abstracts and I do mean at their absolute best more so Strange than Doctor Fate considering Doctor Fate was a Lord of Order. My point is though that unless you load Fate and Strange with their most PIS loaded feats and artifacts there isn't much they could do against CK and I don't think Strange could pull another Shuma style fight. I think CK would corrupt him instantly and it would turn into a 2v1 against Fate.
However that said if they both multigod channel to horrible degrees and essentially channel elder gods, skyfathers and cytorrak level beings then it becomes fairly close. But they would need to finish it quick as I do believe that they would burn out incredibly quickly doing something like that. It would probably be a one shot deal and if they fail then its game over for the good Doctors..
Add Dr. Who and he solos the field given 20 minutes of prep.