Very curious about this too? It almost looks like a scotch tape balance change made prior to release. Was there an issue with it being too OP?
Hopefully it's not and it's user misunderstanding, but I wouldn't mind a dev comment anyway. I think the hero skill definition is HeroSkill06BranchVampirilis.

The simulation descriptor it references... HeroSkillSenator105_FIDSI_PerHeroLevel_3, has a xml comment next to it: <!--FEEDBACKTODO-->

Things are way worse now. I'm getting +4 FISDI per pop per hero level. Basically 90% of empire's income from the skill. To be clear, not 4%, 4 actual FISDI per level per pop. See screen shot.

*Yeah, this particular hero is pretty neat and balanced*

Unless ofc you are playing against him that is.

Just look at those stats +80% dmg, +80% energy dmg, +80% indy, and the list goes on, but last but not least at lvl 30 + 150 FIDSI per pop on system (lvl 3 system has like 10ish slots a planet? hail vodyani!) and +30 fidsi on all others, you would think horatio with all pops spliced is strong, well you would be wrong.

Now imagine if you could score all those vodyani heroes in a democratic parlament.... not hard to get religious/militant going, and then there is eco or science left. Lands you at pretty ridiculous production numbers.

But... why stop there? Heard about the spire of ordained? Oh YEAH +100% xp on assigned hero, now produce couple carriers (you make about 5 carriers a turn even if you don't want to) instant high lvl hero!