Look at it like this, considering you want max profit per level:
Solo: You have to kill all monsters and have to collect all the loot.
Party: You do not have to kill all monsters, but you still have to collect all the loot.
It still goes faster in a party. Now, shut up and party!
(This doesn't consider increased HP from bigger parties, but that doesn't seem to make a big enough difference when you have 4 Blitz knights.)
Right. A party of four faces monsters with about twice the health of the monsters that a solo knight faces, but the party has four times the offensive power, so it should be more efficient.
More importantly, running in a party gets you more minerals...unless that's changed?