Hmmm. I did not have to purchase my Warden separately & I do not believe that I prepurchased Morrowind as I had stopped playing the game for several months before it was released. I did purchase the Morrowind CE, which I believe was called the "Collector's Pack". I also have the slate grey skin & the Warden costume.
Makes me wonder if they granted the class for free until Summerset released, which is kind of a sucky and greedy move on their part IF that's what happened.
OP can verify when they purchased the Summerset chapter by looking at their Billing History (on PC at least). It looks like June 5 2018 was the official launch date for this chapter. So if purchased after that date then one would not get the Warden since they would have Morrowind via ESO+ or DLC purchase.