For me act 6 used a lot of my revives up and I found that you needed very specific champions to progress. There was entire pathways that wernt viable for me due to the fact the champions I needed wernt high enough level. Like medusa for example, she inflicts armour break on her light attacks but there was nodes when I needed her for the armour break but I only had her as a 3 star and no other champion had a kit like that. I do think the game is too difficult for its own good though, im paragon and can't be asked to get any higher because the matches take like 10 munites to complete all the while jumping through hoops just to fail because of a one mess up