People can aimlessly demand AIM-120 all they like. It doesn't change the fact that it's capablities are far above what can be in game right now.
There was no reason whatsoever to not add the Ja 37C when we did and at the time, it performed perfectly fine in its intended role. There was nothing premature about it.
We often add multiple variants if upgrades are possible. See the Jaguar GR.1 / GR.1A etc.
Sweden has options and one of those is to add a Ja 37D variant.