In other words, Solo play should be on the fringes of the sample's standard deviation curve (at the 97.5% would be the upper extreme, which would be where Soloists would apply, whereas 2.5% is where bad parties lie ;50% is where the average party would lie).
If you know nothing about standard deviation, it's a measure of how far from the mean (average) in this case players, can play effectively (deviate from the norm).
Sorry for getting technical. I'm a fringe player and that's my role in most communities. I can definitely play with a team, but over the long term I find solo-beating teams much more enjoyable.
First of all, I don't think soloing the world bosses should really be an indicator of a class's soloing potential; I know that you're not suggestion such, but just wanted to throw that out there.
Each class is supposed to not just have benefits, but also drawbacks associated with the class. Sure, it would be great for the SM players if they gained the infinite MP capabilities of a sorceress, but think about where SM stands in the balance of other classes for a moment: SMs are defensively up there with the ability to heal themselves without worry, they get AoEs pretty early on in their careers, and are very capable of solo AoE grinding. The biggest downsides right now are that they do a bit less damage than sorcs and that they need MP pots for continuous grinding.
If you give a SM the sorceress's MP regen abilities OR power that outstrips the sorceress, think about where the sorceress currently stands. An SM can heal and has defense/HP buffs pretty early on, so they are defensively superior to most classes (save paladins at the level 35 cap). With power, an SM can now do more damage than sorcerers with the proposed buff; this, added to their already superior AoE capabilities, means they are now the best in both offense and defense. With a sorc's MP regen, a SM is now the only class that does not require any consumables of any kind to solo temple 3, while still being a defensive powerhouse and a very good AoE grinder. How, exactly, does either of these bring balance to the game?
I really suggest that all potential changes be made with a look at the general class balance in mind; every class is supposed to have some aspects that they shine in, and other aspects in which they are not as good as other classes. Most people in all four of these forums (sorc included, actually, despite how universally reviled they seem to be) will only suggest buffs to their class without caring about overall balance, and if paladin/SM weaknesses are removed without a consequential adjustment to their strengths, that would be pretty darned bad for the game overall.
@divvsy: Don't be so harsh on sorcs =p. They can solo floor 3 with mixed AoE's and ST pretty well with quite a bit of care, even if they need to gulp down HP potions to do so. Especially if my almost full left tree sorc can do it...