That seems a bit dramatic. I think there’s a point where too many damage types actually hinders buildcrafting. It makes class synergies more complicated and more difficult to parse for the typical player. It also means that each damage type doesn’t feel as unique.
To combat that to a degree, we’ve leaned towards having damage pairs that are frequently seen together (ex. Chaos and Vitality, or Cold and Lightning). Conversion helped as well.
I’m not convinced that culling some damage types would hurt build diversity. I think it would make your choices feel more meaningful, which is why if there is a GD2 some day, it will definitely be a step we will be taking. Most certainly you would see flat and dot damage share modifiers. Elemental would likely be removed as it only complicates things and requires additional explanation.