By how much are the Blades of Exile and Athena superior to the Blades of Chaos? Are there sources that state that they are much more powerful?
The Olympian > Titan > Primordial scaling chain should tell you of their superiority to the Blades of Chaos, that and Kratos literally fights against the Olympians using them. You really don't need statements at that point when you literally have the feats to show for it. Plus the Ares boss fight says it all, where most of Kratos's weaponry was barely making a dent against Ares' armor (In the novel Ares' armor is stated to be tough as nails and really hard to pierce through) and Kratos needed to use Ares' own spider-arms against him to deal any significant damage to him, and only the Blade of the Gods was strong enough to overwhelm Ares' defenses. Novel also states the Blade of Artemis, an actual godly weapon, to be far stronger than the Blades of Chaos verbatim, Artemis even stating that she used it to kill a Titan (This statement is both in the game and novel). That and the Blades of Athena are 100% of Olympian origin instead of being of Primordial origin, to serve as a replacement for the Blades of Chaos that he lost.
As for feats?
1. Kratos used the Blades of Athena to destroy Thanatos
2. Kratos used the Blades of Athena against the Titans and they could easily withstand the Rage of the Titans being poured into them, as is the case with Kratos channeling his powers into the weapons he uses. He then uses them against the Sisters of Fate, and then against Zeus wielding the Blade of Olympus against him.
3. Kratos uses the Blades of Athena against Poseidon and his Hippocamp, easily cutting down through them.
The Blades of Exile are even superior, considering they survived the corrosive waters of the River Styx that ruined the Blades of Athena, they could easily hold their own against Hades' own Claws, go toe-to-toe with Hercules' Nemean Cestus, and was used to give Zeus a vicious beatdown in GOW3. It was also the only weapon to survive Fear Zeus's full powered lightning blast alongside the Boots of Hermes, every other weapon Kratos had on him got trashed forever. Kratos then used the Blades of Exile to channel Hope through them to trash Fear Zeus effortlessly, not that Kratos needed them since he was basically a brick wall to Zeus and effortlessly blocked a punch from him.