It depends on who/what you're spending that € on.
They have dozens of partners, where it's 2.5 miles per € and a handful of major partners, where it actually is 5 miles per €.

Revolut's "change-to-points" system leads to a purchase price of 0,02€ per 1 mile, which is marginally better than Aegean's own standard rate.

There's also a -25% less miles promotion right now for award tickets within A3/OA, which may sweeten the earning rate a bit.