Yeah, when I played Y for the first time, I never used Aegislash since I didn't know it even evolved and just ran with Duoblade for the whole game. TBF, as far as middle evolutions go, Duoblade is probably one of the best ones since its stats are pretty min-maxed.
Speaking of Aegislash, I hate how it was nerfed. You'd think the Sword and Shield Pokemon would be buffed in Sword and Shield,, but I guess that made too much sense. They nerfed its stats, its signature move, and w/ Dynamax since it is one of the weaker Dynamaxers out there due to not being able to use King's Shield. I don't think any Pokemon has been nerfed to the extent Aegislash was. Other Pokemon that were nerfed, like Mega Khangaskhan, only got a nerf to their abilities or moves. However, Aegislash is the first Pokemon to have its stats straight up lowered, on top of its main move being nerfed.
What also sucks is that Aegislash didn't really get too many new toys in Sword and Shield either. Steel Beam and Close Combat are cool, but both moves have severe drawbacks. Other moves like Poltergeist or new coverage from a move like Leaf Blade would have been a lot more interesting I think.