Once your sovereign has magic champion armors that give 1 strength / dexterity / constitution per level, then the paragon spell no longer reduces those stats off the sovie and you can cast it with no limit except your mana supply.

Of course, I'm having too much fun exploiting this to do anything silly like ask them to fix it       I currently have a hero at level 90-something.

The fact that you could get up that high has been reported before, as was the fact that heroes with enhanced intelligence can gain more than 1 level per cast  (I've seen up to 3 levels at once), but I don't recall reading that that champion armor was the key to getting it.

As your champ gets to insane levels, you eventually get all 5 "Paths of the" and all possible traits.  Then all you get when you cast it is a level, although you still have to click "ok" on the empty chose-your-trait screen.  You get there with fewer casts and less mana consumption if you start with a smart guy and pick Path of the Mage early on because it increases intelligence.

i stumbled into this late-game.  Next time I might try researching straight to championship armor, then passing all my intelligence-enhancing rings and skull-caps to my smartest champ and go crazy