you hit the nail on the head
knowing the quests is huge, and knowing them well may take dozens of runs or more
Gear is the key. After a few heroic lives, your bank is bursting with the 'right stuff' While new players don't have that luxury. The right gear at cap, can take months to get solo. Even if grouped up, newer players wont know what they actually need.
A 1st life character can be set up to do r1-r4 ...but it takes a veteran ddo player set up a character to do that. And it definitely takes a Vet to push past those skulls.
Vets can only help so much with newer players unless you static group with them. I always end up helping a few random players graduate into r1 each life. but, its way to common that their character is built for hard difficulty...and we wind up carrying them more than helping.
Those 400-600 hit point characters trying to do epic reaper can only take so much before they slunk back to soloing hard or just move to another game. There's just TMI to relay to random players in a few tfo's to get them to build a more effective character.
Playstyle goes a LONG way too in DDO. How many times will someone let themselves get surrounded and die before they try a different approach to a mob