I am not sure how things would be different if IGA isn't around. The castlevania games are still fun even though I would like a return to the pre SOTN days. However, what counts is how enjoyable the game is.
It would be quite difficult for me to fathom if the CV games are handle by another company other than IGA or Treasure(some of the employees fro that company did the pre cv games.)
In the case of Contra, a lot of the titles not made by konami sees to be either crap or missing something.
Wayward's Contra 4 is a nice return to the old style, but after beating the gae in hard mode, I realize I don't want to play the game a 2nd time unlike Contra 3, which I play over and over again. I think it has to do with the innovation of the game since I felt that nothing really wowed me in contra 4 like it did in contra 3. True, contra 4 brings in grappling hooks and a vertical screen, but the grappling feature was used in other games better. I cannot point my finger on it, but I felt soething is missing in contra 4.
I mean, there is still things I would like to see in CV, but it is getting there with the sequels and I would rather have someone who have worked on the series for a long time than a completely new team and see whether or not their game works or not.