Or as one suuggestion has said, all the individuals in a group can offer up mats at one time (so if a boss needed 5 living steels to summon, then everyone pitches in 5, for a total of 20) and bosses drops 4 summons worth of loot (so instead of summoning 4 times, you just get it all in one summon).
Another suggestion of the same vein was instead of 4 summons worth of loot, you get a a better chance at the rarest drops (so maybe doubling/tripling the chances).
As it stands, i hate grouping up. So time consuming
Edit: time consuming for an ARPG. I use to raid lead in WoW (especially pugs), so im use to blocking off time for an activity, but thats for 1-3 hours, not… this.