Canon may not be violated if the simulation is only optical and not physical. It could just be holographic. We did not see any physical contact with the Klingons, just phaser blasting. Nor did we see collisions with walls, etc. But of course we didn't see holographic simulations in TOS either, and Discovery is supposed to be ten years before TOS. But if STD only had TOS tech, we'd all be bored. I'd rather have things like holographic displays, than primitive TOS displays, and "bend" canon a bit, or just attribute it to some kind of parallel universe reboot. Also, the USS Discovery is an experimental ship, so we could say that NCC 1701 might not incorporate all of the tech of the USS Discovery. Canon is a mater of linear timeline events. With Star Trek constantly featuring time travel and alternative universes, maybe we should afford some time-bending flexibility to the sacred canon concept?There are no words for tonight's episode? Holodecks are not supposed to exist in this timeline. Writers do not give a shit about canon. Canon be damned!
http://memory-alpha.wikia.com/wiki/Holodeck