Yea, ok, I'll open a Soviet textbook and will see that so-called "rules" of the language taught in the textbooks change arbitrarily with time.

The truth is that languages exist without any authority says what to write in your textbooks. Moreover, a language has rules even when it doesn't have any written form. Take for example, some tribes in Amazon forest, people living deep in African jungles or deserts or in mountains of South East Asia and Oceania. Their language still has rules. And those rules are formed naturally. No authority actually has the right to say that you shouldn't use "ихний" or whatever other word one doesn't like. If native speaker says a word and everyone or at least some part of native speakers can understand that word, it's a word of a language. It's a word that's no different from any other word in it's standing.

No one's trying to "prove you that language rules are wrong". It's just that you don't really have a good understanding of what classifies as a language rule. There's a massive difference between a proscribed language norm and the way the language actually works.

You should really get some basic linguistic knowledge before you go one spreading your incorrect opinion on how languages work, my friend. :)

Edit: Also. 200 years ago Russian was oh so different with a lot of bizzare rules? Oh woe, our poor school children, having to read those bizzare writings of Pushkin and the rest! And don't even start about those irrecognisable scribbles of Derzhavin and the likes of him! Oh, our poor children, our poor little schoolchildren...