Maybe they did make a mistake, but if so they can fix it. I think what the court majority is saying here is patronizing and wrong. There's a perfectly normal process for Congress to amend a law if it accidentally gave up too much power.
I prefer that matters like this be handled in an actually democratic way. Cannabis was legalized in my state because I and others in my state voted to make it so. That's democracy. Technocracts making unimpeachable "scientific" decisions isn't democracy, it's a faint shadow of democracy. Referendums are democracy, and are the democratic way to resolve these sort of social disputes.
When your state legalized marijuana, it delegated a ton of decisions to unelected officials - individual business licensing, labeling details, dispensary sanitation standards, valid medical applications, etc. There is probably a whole commission of unelected people who go through a formal rulemaking process which involves collecting feedback from people like you, just like the EPA.
It's ok if you don't like this model, but you can't claim it's not what Congress intended and not a normal state of affairs at the moment. It's just how the country works, we don't have Congress vote on every single pollutant, medical device, potential drug, import/export restriction, endangered species, etc.
That is the matter of contention, isn't it?