Group penalties: XP is the first. /5 and a 25% modifier means it takes 4 kills to = 1 kills xp if solo (with a 5man group). And no with 5 people you cannot kill things 5x as fast. I wrote a rant about this a while ago with a simple calculation off of the global cool down.

Game to compare it to. Asheron's Call. Past a certain level (50 I think) everyone was treated equal in grouping. Also xp was not divided up by how many people were in the group. 2 people I think each person got 75% of the xp. not 50%. And it capped at like 33% even if you kept adding more people to the group well past 3 people as wow divides xp by.

Fixes: Allow mentoring down like eq2. Increase the group xp bonus by 100% at least. Remove xp penalties past level 60 if grouped with higher toons.

Questing: Collection quests, need I say more. It makes no sense when asked for 5 doohickeys to make the summon item to kill the bad guy to need us to collect 25. yet only have one guy summon and kill the bad guy for everyone to get credit and the rest just deletes the summon item. All collection quest items should be group lootable. This is 100% a penalty to grouping.

Grouping should always be faster and the preferred method of playing, but its not. You are penalized by grouping until you level cap and the only way to advance after that is group content in instances.