"Besides the elementals, the only known sentient races on Azeroth when the titans' forces arrived to subdue the Old Gods were the trolls, the race known as "faceless ones," and the aqir."
Proto-dragons were a lot dumber than current dragons, but they were still sentient; capable of rational thought and speech.
Just gonna chime in the dog and wolf argument. Humans allowed wolves to come to their camps because they could detect lions or sabertooth cats approaching the camp and eventually a group of wolves became tame and began to live entirely amongst humans and the tamest wolves were the most likely to reproduce while the humans could take down a mammoth and could easy feed the wolves the scraps the humans couldn't eat. While cats came from agriculture. Soon as we began storing food, pests became a problem, so we began to tolerate having the wild cat species from the desert in our silos because they killed the vermin (perhaps the pandaren should look into this idea =P). Over time, the cats that got to benefit from our ability to attract vermin were the ones that we tolerated, hence why traits like meowing and the kitty seductiveness came about. Dogs and cats are the only domestic animals that came about natural selection (at least until we started making breeds). It's the animals like goats, sheep, horses, cattle, etc, that have been enslaved. They typically are not privileged enough to come into the house.
Anyhow, to the OP, that really sounded like a good theory until people presented evidence that the Pandaren were around before the Mogu empire. The Mogu failed if they created the Pandaren because they created them with emotions that made them hate slavery. Dogs and cats aren't slaves because they love us. We can open the door to let them out and they will come back. But the pandaren were given very human like emotions. The idea that the pandaren were created by the Mogu was interesting and would be a great twist and I think it is kinda plausible. Pandaria lore continues to grow more and more interesting.
At the time of the dev chat, proto drakes probably weren't considered "sentient;" all the in game ones were merely beasts (most were even classified as beasts)
The running theory up until... well, pretty much now, was that proto drakes naturally evolved from dinosaurs and eventually into dragons.
When they wanted to write "rise of the aspects" with the original aspects as proto drakes, they probably didn't "oh gee, that'd be cool to do, but in that one single dev chat we didn't mention the proto drakes were sentient beings, so I guess we can't"
And besides, the dragons seemed to have gotten a pretty good deal out of the titan's arrival.
“Do not lose time on daily trivialities. Do not dwell on petty detail. For all of these things melt away and drift apart within the obscure traffic of time. Live well and live broadly. You are alive and living now. Now is the envy of all of the dead.” ~ Emily3, World of Tomorrow
Words to live by.
But haven't we been fighting on the wrong side since Algalon, in Ulduar? Wasn't he a servant of the Titans?