For me: normal and hard are both easy, and is fine so, just they should have to be a bit more different, if i don't read on XP table the difficult i cannot find any notable difference.
Elite: i'm fine to zerg (with some diffs sometimes), but if i find a trap i die: monastery of the scorpion traps: 44+11= fail O.o how should i have 55+ reflex on heroic? Yesterday an arti with evasion and insightful died 7 times to disable von 5 traps (yes some ppl was healing him). Traps can deal 100+ damages at lvl 5 and 300+ at high lvl heroic. My suggestion is: yu can strong a bit more the mobs (expecially bossess that can be shotted expiacially at low lvls), but nerf a bit the traps.
Scaling: last TR i run Elite invaders on a full party, ice reaver was dealing 200+ from polar ray, we wipped. I did it again in solo, this time they deals half and was easy. Now: what's the point to have a party if soloing is easier and faster? Usually i join in party just if splitting is a great advantage and just with good ppl, for the rest i prefer to solo. Great scaling = less party. My suggestion is to modify scaling, is fine if mobs got more HP (DPS is supposed to be higer), is fine if mobs are more, but the damage should not increase by 100% expecially for the skills/spells that can shot ppl.