I don't know why you weren't expecting a stronghold this pack, they explicitly stated there would be a stronghold in the last pack in an article a couple months ago. And when there were a bunch of rumored uni cards that included several that were later verified, one of them was a stronghold with mechanics very similar to the lion stronghold. The lion stronghold is the name of a location that is in contention between the lion and unicorn clans right now in the stories (at least, so I've heard, I haven't really been keeping up with the stories due to the annoying absence of the dragon clan in them), therefore a lot of people theorize that the stronghold in the last pack will be a uni stronghold with the same name as the lion stronghold and a similar mechanic.
Also, as for the numbers thing, not all of the clans had an equal number of cards in the core or the imperial cycle, so clearly that isn't something the devs care all that much about so long as it's close enough, and they explicitly stated that fixing uni was a design goal for this cycle, so having 1 more uni card than anyone else would make sense as far as that goal goes, and given that the stronghold is something that a lot of people says is part of why uni does so poorly (personally, I think once there's enough cav peeps it will be a decently powered stronghold, but that's just me) a new stronghold for uni makes sense. Dragon getting a stronghold here doesn't make much sense, as much as it would make me happy if we did, as we're in the top three clans, and our current stronghold works decently for both our current deck themes, voltron and monks, so giving us a new one wouldn't accomplish much other than maybe push us to simply dominating the field (assuming it was a better one than the one we've got).