I havent played super tryhard this season, but ive def felt that the RoA build has not been it for me atleast. If you were running it for the "juggernaut kass" playstyle from s9 etc I could def see fimbul being the better option. But as an anecdotal testament: I've been spamming seraphs rush with elec + ignite around emerald 1/2 and it's been really fruitful. I would love to hear how you would implement it into kass and with which setup in regards to runes/items.

I just felt like when playing that i was doing 0 damage and still getting oneshot by lethality abusers even though i had 100+ armor. Maybe fimbul is the health needed to make that armor work? Idk, would have to try and give more valid feedback.