Is there an antonym for nihilist?

I'm specifically thinking of nihilism as defined here:

Nihilism is the philosophical viewpoint that denies or lacks belief in any or all of the reputedly meaningful aspects of life.

Not nihilism in the pessimistic sense, but rather in the sense that a nihilist doesn't have specific beliefs, or thinks having specific beliefs is futile. The definition of this antonym would be something like:

Someone who has specific convictions, positive or negative, on a given subject.

This word shouldn't be constrained to morality, but could apply to any field (e.g. religion, philosophy, stock markets). Opinionist is a promising contender, but doesn't quite work because it typically connotes someone with contrarian views. Conceptually, it would be something like specifist or convictionist (these aren't real words).

Sample sentences:

Unlike nihilists, ____ have specific beliefs.

The decline in active investing suggests there are fewer ____ than ever in the market.

Solution 1:

I suggest "believers":

• The decline in active investing suggests there are fewer believers than ever in the market.

The first sentence would require changing "beliefs" to some other word:

• Unlike nihilists, believers have specific convictions.

Solution 2:

The word antinihilist actually exists, as such.

Etymology anti- +‎ nihilist

Noun antinihilist (plural antinihilists)

(philosophy) One who opposes nihilism.

Wiktionary They even have an Institute :

Welcome to the Anti-Nihilist Institute

The Anti-Nihilist Institute