Honestly, the bosses would need much better mechanics that eliminate the ability to cheese. Currently all bosses can be hurt at all times. If someone is able to exploit the AI, and get enough DPS, they can solo a boss. AI is very hard to get perfect. Most games with bosses get around this by utilizing mechanics, that force you to move around, and interact with the environment, to prevent cheese strats.
The lich boss has some mechanics that do this, but its far from perfect atm. As soon as you make these mechanics require more than 3 people, the boss will almost never be done. Few people will be able to go down, and find another group that want to do the boss, and then wont kill eachother over the boss afterwards. It just leads to feelsbad situations.
As for loot density, it can go either way. If the portals are all within close proximity (as they were in goblin caves) I often ignored people that were not directly interfering with my objectives early on, and let them gather loot, and killed them at the end to collect their hard work. I focused on champions for high tier loot, then let other players deliver trinkets to the portals. This worked well, as I was a plate-fighter, and could force players to come to me, instead of forcing myself to chase faster players. So, in a way this seems to be both what you were talking about, and what you wernt. There can be strategy in letting people live and not bumrushing them. However it depends on how well you can secure portals you are confident will get your team out.

Gamers, there is always discussions/polls on what makes certain classes strong but I really want to know the weaknesses. What class have you played the most of so far and in what ways was it hard countered? Bonus points if you explain your build its pitfalls as well.
Fighters - Either well rounded builds that are great at nothing, but have no glaring weakness, or monterous physical tanks, that are slow and weak to magic, or rouges. The tank build hard counters Rangers>Barbs, but is weak to Wizards and rogues. Clerics and other fighters can go either way.If you want to learn more about Dark And Darker,please vist mmoexp