You’d be replacing some problems with other ones. With an auto-calculated figure, users will have no insight into what the calculated figures are, and won’t easily be able to adjust them when they e.g. merge decks from two profiles together.
The setting is already in the advanced section, which is exactly where such relatively-obscure settings belong - people who really care about it can still tweak the value to their desires, and the bulk of users can just ignore it.