Crossovers are not considered a good source regardless if they are supposedly in continuity. There were too many arguments and reports stemming from the JLA/Avengers crossover. Characters have enough appearances w/o having to resort to crossovers between 2 separate companies as proof.
There's a large difference between crossovers from 2 separate companies and crossovers from the same company. Politics about characters, status of characters, etc. plays a part regardless of any implied continuity. Could Superman beat Thor or could Thor beat Superman if all things are equal, sure. They are close imo. Will Superman lose to Thor in a Marvel/DC crossover, nope. Superman is far too popular.
The Serpent, the Meggadon Wheel...they all have their obscurity due to hyperbole and fanboy induced hysteria. Nothing can be done about that except to acknowledge that the feats occurred and try to form a rational opinion based on the art and dialogue.