There should be no real hard cap. Keep everything as is, but you can put 400 points in each category. And reduce the mainstat/vit you get after spending 200 points into them to + 1. (So at paragon 1600 you got the most value)
Or +1 from the start.
So the power cap between casuals and hardcore blasters isn’t that big.
Another approach could be that you need more paragon points after you spend 100 points into something. So it gives a little more value to other stats.