Obviously this is a very simple way of balancing the game. Unfortunately, it runs into the same problem of balancing between monsters.
Flamespyre Phoenix is absolutely ridiculous. It is the best monster by a landslide. With your method, you are assuming that all monsters are equal, but they are not.
I like your idea of limiting war scrolls, and we will probably see this at some point, but I think the only way to balance this game is to add point costs.
http://ageofwargamers.blogspot.se/2015/07/ppc-age-of-sigmar-army-lists.html
This is a link of what I have been helping a few other people on this forum. There are also many other groups of people developing their own system. Just surf the web and you will find a system.