Tip to the ones who will fall into the trap: 10m raids existed before 25m raids did.
As far as I remember, all of the original instances that we now call "5-mans" (including Scholomance, etc) used to be able to hold 10 people (even if the quests only gave you credit outside of a raid). However, we didn't call them raids. We called them instances. Even Upper Blackrock Spire we didn't consider to be a raid, and we could originally take a full 15 people in there.
That's actually the reason why I can't take 10-mans seriously as raid content. It's just instance grouping to me - and smaller than the UBRS instance that we PUG'd out of the server's general chat. The small-scale content doesn't feel epic to me. I know that a lot of people really love 10-mans, but as someone who enjoyed raiding 40 mans and was already bummed when they down-sized to 25, I just get no real enjoyment out of 10s.