"By so much" indicates the measure by which he evaluates people.
By "acts the better part" he means "acts seriously", maintaining a serious face even when they feel happy.
This may be confusing because Hall is speaking from a religious perspective, using a card game as a metaphor. In a real card game maintaining a poker face is a virtue.
Anyone who thinks a poker face indicates "the worst kind of player" (as opposed to "the best") would lose at such games.