Scenario 1 Medaka wins. Hades is way too fragile for his own good, and without Agyo Shaka isn't really that strong.
I'll give Scenario 2 for Hades. One thing people need to understand about Cosmos is that their resistance against Hax is insane. They can pretty much nullify any and all such types of abilities if their user is of a lower or similar level of power. Case in point:
- Ikki nullified Shaka's "Cycle of Six Existences"
- Rhadamanthys nullified Deathmaks's "Sekishiki Underworld Waves"
- Sensory loss negated by high level Cosmos
- Mu's Universal Range Psychokinesis abilities being rendered useless by Saga, due to his higher Cosmos
- Countless exemples of escaping illusions and alternate dimensions and mind attacks
- In Omega high level Cosmos Users are abe to endure a universe space-time stop, and defeat a guy who made it so that outside time wouldn't affect his atoms, so he wouldn't take damage
Alongside that, his speed is insane. He is not only Quintillions x FTL, but likely at least Sextillions.
Case in point: Pre Seventh Sense, at the peak of Base Cosmos, Seiya is Mach 1 at least, and at least around Mach 20 at most, then with Seventh Sense he goes to around freaking Mach 881,000 (Becoming FTL), with Eight Sense he is MFTL, and with the wings grown due to Athena's blood, he was Quadrillions to Quintillions x FTL in short burts (He was exhausted when he arrived in Elysium). Thanatos is fast enough to blitz Seiya with wings, and God Cloth Seiya is too fast for Thanatos to react. Then we have Hades, who does the same to the God Cloth Saints.
Considering the level of speed progression from one level of Cosmic Power to another (Mach 1 to Mach 20 > FTL > MFTL > Quintillions xFTL > ??? > ??? > ???). The speed Hades has at full power is insane.
Also, answering Sin: Most of their stats do indeed have combat functionalities. Like swords that can rip space-time, a schyte that in seconds reverses space-time until the atoms of the opponent have all their history rewinded to before the Big Bang and erased completely, characters who would shatter the universe, or who's mere presence englobes the universe in their Cosmos, etc.