More Destroyer Models?
What we see now are basically the expendable footsoldiers of the other Elder Dragon’s army. It’s like how you only really see thralls, brutes and the odd abomination outside of Orr or when Zhaitan sends an army to attack an area.
The dragons seem to hold their elite troops close to them, and we havn’t gotten anywhere near the other dragons’ territory.
Still, look at the variety of Risen there are. The Icebrood and Branded also have a good amount of variety. The Destroyers, 3 models and again with a 4th only found in Sorrows Embrace. Anet could have taken the time to make other types of Destroyers.
For as few kinds of Destroyers as there are, I can’t say I’ve ever paid much attention to their lack of variety. Most of the places where they do show up feel like they’re overflowing from under the earth (or Mount Maelstrom,) rather than having established their own, permanent territory like the Icebrood, Branded, and Risen have. It’s natural that we’d see a lot of Risen, since we march straight into Orr.
Meanwhile, we haven’t gone far enough north to reach the Far Shiverpeaks or far enough south to reach the Crystal Desert, the homes of Jormag and Kralkatorrik. It’s possible the Dwarves, or what remains of them, are keeping the Destroyers busy in the Depths of Tyria, which is why we see less overflow into the overworld, if you’d like a lore-based reason why there aren’t more Destroyers.
And if it’s any consolation, they did change the Megadestroyer so that it’s not just a giant Destroyer Troll anymore.