I would argue, that this is easy to fix: Give them a new ability every 8-10 sessions. We play once every four to six weeks, so we are happy with the regular suggestion.I have a feeling that if characters gain a Heroic Ability every five sessions, my group will have a dozen Heroic Abilities in no time (we play weekly, planning on an ongoing campaign).
I really hope that FL does not switch to a normal point buy system. Yes, we know it from thousands of other systems, it works and we love it. But we also know it from thousands of other systems. Granting a new ability every X sessions is sweet, and a nice take on the 5E milestone system for level-less advancement.
But maybe you want to add a Designer’s Note-/Optional rule-box and explain how easily one can adjust the advancement tempo by changing the amount of sessions needed?