Lets talk about how making group bosses scale linearly with number of players often doesn't make for good content

Zamorak, Hermod, Vorkath, and now Sanctum are all bosses which you can fight in a group, but the health and mechanics scale linearly with the number of people. By linearly, I mean that if you double the number of players (from 1 to 2), then the health of the boss doubles, the number of mechanics doubles, and the health (or number) of minions doubles. As a reward for this increased overall difficulty, everyone gets the same loot chance, regardless of number of players. This is in contrast to bosses like Kerapac, AoD, Vorago, and Elite Dungeons, who do not scale at all (or very minorly) but there is a fixed amount of loot to divide up between players.

I believe that linear boss scaling is not often a good design decision. There is always the social aspect of bossing, and a benefit for you to group with someone who does higher damage, but what motivation is there for them to group with you? If two players can fight the boss separately with approximately the same difficulty as if they fought together in a group, then the pros and cons of grouping up depend heavily on the specific mechanics of the boss and how players can interact with each other.

For example, at high enrage Zamorak it is beneficial to group up, since intercept-defensives can be used to mitigate large amounts of damage. In contrast, at Nakatra it is easy for one player to mis-step and die to a mechanic that cannot be defended against, which leaves the other players to then have to take up the slack from missing a person. At Vorkath it is useful to have separate players take aggro of Zemouregal and Vorkath, but the minion health rapidly outscales the damage that the balista can do, because the balista does not scale damage and shares cooldown between players.

In my opinion, the best method of scaling a boss is that which Solak has. The health scales with 'number of players + 1', so that having more people means each individual has to contribute a bit less damage overall, but with diminishing returns at higher group sizes. You still have to deal with more mechanics and higher health minions, but if you lose a player toward the end then its not as big of a dps loss to have to make up. It gives players an actual incentive to group together, after all the second M in MMO is for muliplayer.