As has been said, OSes are hard to get rid of, completely. Even Smash has OSes (though I haven't heard of useful ones, outside of one I came up with in Melee). So why not teach them to players in the tutorial? The awesome thing about Xrd's tutorials is that they give you not just a more fundamental understanding of Xrd's systems, but FGs in general. You can take what you learn about OSes, Reversal timing etc., there and apply them elsewhere because they're constants of the genre. The game does not introduce them as constants, but still. The greater evil is to keep fresh players in the night regarding them, completely, imo.
I don't think OSes "dumb-down" anything. In fact, they help players get to the meta faster with just a little bit of executional refinement (which is what people of these types claim to value so much). They make the conditions simpler, by narrowing the possible outcomes, making the mind game element stronger. That doesn't make for a "dumbed-down" situation at all, as long as there's still a tactical response to every possible outcome, whether those involve OSes or not.
If your intention is to play Rock & Scissors together and the game allows you to do this, the game isn't choosing anything for you. You're conscious of the options being selected. I see it as no different than entering a command for a special move or special normal, etc.
