The level of maturity in argument here is astounding.

Your example is fine.

"Here" is an intransitive locative preposition (in this place) contrasting with "there".

Its function is that of post-head modifier: it modifies the whole NP "the level of maturity in argument".

The level of maturity in argument here is astounding.

Your example is fine.

"Here" is an intransitive locative preposition (in this place) contrasting with "there".

Its function is that of post-head modifier: it modifies the nominal "level of maturity in argument".