I think you missed the point I was making.

Lets even just look at a basic Fireball technique of a decent size. Not only does that provide cover in that you can obscure yourself (or objects) behind it allowing for certain amount of in combat adaptability, you can use it to create damage to weak points on structures, or to start a forest on fire in combat to give yourself an advantage.

An illusion is just that - an illusion. You can't use your Genjutsu to destroy something to give yourself an advantage, you can't really do much other than alter the perceptions of your opponent; which is something that can be largely grouped together under a singular technique solely by being vague about it. I used to have more techniques on my characters such as Touzoku and Chiyoko mostly because I went specific with my medical techniques. However, I found that to be tedious after awhile as it is easy to overlook something. Thus I created Souken to fill that gap, as I could adapt it to suit a number of my needs.

Genjutsu lack a certain adaptability in combat unless they are vague - specificity only breaks something that could easily be one technique into a bunch of smaller ones, which is largely a flavor aspect of things.