The reality is that there are often several different ways of notating something, and this doesn't just apply to key signatures. Often the alternatives are entirely logical, and work. However over a long period of time a standard way of doing it has arisen. Conventions are useful because they lead to consistency. The concventional approach to key sigs doesn't immediately tell you if its major or minor, but it is a standard approach that lets you sort out what they really mean very easily.

That doesn't mean to say conventions should be followed slavishly, but if you deviate from them you should have a very good reason, and be aware that you're likely to cause as much confusion as you prevent.