We appreciate the feedback. For what it's worth, we don't really look at it this way. The way we look at it is, Hades is approximately 3X bigger and substantially better than it was a year ago. We think it's worth more, not less.
If we were offering the same exact game we offered a year ago, I would 100% agree with you (if anything 30% off would be too low). However, we've been actively developing Hades in Early Access, and adding to and improving every aspect. For example, just this week we added more than 2,000 new voice lines to the game to further deepen the story, along with a variety of new and improved systems -- to put that in perspective, Bastion had about 3,700 voice lines in its entirety.
So, rather than thinking of Hades as a year-old game, I hope you'll come to think of it as a new game that keeps getting better while it's in Early Access, until we finally hit our v1.0.