Of course, you can play without rules, but after a certain number of games, you realize that, for example, groups of Phoenixes or groups of Vampires are overpowered, hit-and-run tactics are also overpowered, and the Cartographer is just too good. Taking objects from under guarded structures also doesn't seem quite right, and so on. All the rules were developed and refined over the years. It's not that complicated if you take the time to understand them.