At this point, grouping seems like a punishment. Even just a two person group cuts your materials in half. For lower star materials this isn't really a huge deal, but in a t3 run when usually about one five star mat drops or once in a blue moon when an actual piece of equipment drops it is soul-crushingly depressing seeing it to go someone else. This is especially true if someone just joins in in the middle of your run or something, but just in general it seems like a really flawed model.
On top of that, grouping doesn't even seem to make most things easier. There are a few points where you can do things more efficiently in a group, and in return you are stuck in a situation where even if you are grouping with competent people all of you end up shield bashing monsters around in ways that are unpredictable to other players, and monster's movements are more unpredictable because they have more targets to go after. Obviously being able to revive one another is a significant boon, but the fact that monsters have more health and are less predictable makes the need to revive more of a feature that brings the difficulty in line with soloing, rather than making it easier.
Perhaps shifting it so that there were a fair number more monsters with a little more hp instead of having a few more monsters here and there and a fair bit more hp would help resolve the issue. This would increase the number of materials that drop, so that it is more likely that both players can come away with something decent. Having some sort of round robin option for loot could also help, with loot stratified by star so that if one person got a five star item, the next one to drop would go (randomly) to one of the remaining people in the party that had not yet gotten a 5 star item until everyone had a five star item and the process would repeat itself. If the excess crowns and heat given out with more monsters in the game were an issue the way crowns and heat could be changed to split evenly between players (like if a five crown coin dropped with two people each would get 2.5 crowns, or alternate between giving one player three and the other two.).
As it stands, while I do enjoy playing with other people it really grinds my gears when a friend joins in the middle of a run and then they end up getting more value out of the run I have been working on than I do. Perhaps that makes me a terrible person and I should just be happy for other people, but I feel like the game could handle grouping better than it does.
I used to think this way, but it turns out that when you group with moderately competent people it greatly decreases the amount of time it takes to run different areas. When solo, it can take much longer to kill enemies since you inherently have aggro on every single enemy you encounter, while when playing in groups you can juggle aggro and output a lot more DPS (with less concern that you will die and have to spend CE since your teammates will resurrect you!) Since you get the same amount of heat and crowns as when solo, this usually makes grouping much more effective (if you time your runs you will notice an extremely significant decrease in time when working with (again, read: competent) groups. This allows you to do more runs in the same amount of time, (probably at least two or three times as many) so if you're worried about getting items, while it reduces your chances of getting an item in one individual run (while grouping), you can do many more runs in the same amount of time and the loot generally balances out.
Two cents.