FSRS has dials to tweak to show you cards either more or less often, so if it's feeling "too hard" you can tweak that dial to show you cards when "easier" (at the risk of seeing more cards per day since you're seeing them more often).

Failing to do that, one might consider that instead of focusing on how hard each card feels, but rather the size of the corpus that they have "under their belt". This is the case if you're constantly adding new cards - if you are and your cards/day is stable, then you have an ever increasing mound of memorized knowledge.

If you aren't adding new cards, then the cards/day will inevitably go down, barring some actual cognitive issue.

It's a matter of what you focus on as your measure of success.