I think maybe the problem on the "too easy" side is more like "too streamlined." They did make a lot of strides toward giving the bosses of the light-party dungeons more attack patterns and movement, and they are harder than they were before 7.0. But despite being a bit more challenging, nothing has changed about the structure, and outside of a couple specific attacks all of the patterns have been seen before. It's still just three bosses broken up by exactly eight groups of regular mobs that can be grouped up in pairs due to walls, and players still use their AoE rotation on the packs and their boss rotations on the bosses while dodging the patterns they've seen so often they're likely to just guess that a donut will be followed by a circle, 180 will be followed by -180 on the first try.
I definitely agree there needs to be a better balance and more content in the middle grounds (which is honestly exactly what CEs and CLL/Dalriada were before), but they also need to mix things up and stop sticking to the same formulas for everything all the time. Every expansion it's 10 levels across six new areas, six dungeons, and two trials. Every time we have to get the same number of aether currents from quests and finding them to fly. Every patch cycle has three allied societies, which have been further codified into the same combat/gathering/crafting every time. Every major patch has either an alliance raid or a full-party set with the exact same tiers of equipment obtained in the exact same way. And then after adhering to the strict formulas, there's barely any room left for anything new and we get "not enough time or resources to make two versions of Forked Tower." This is the problem from which all other content problems stem.
Put more simply, the issue isn't that they didn't make Vanguard or the Shadow Lord more difficult enough than Ktisis Hyperboreia or Nald'thal, it's that other than the difficulty changes and different boss attack patterns they might as well be the same place despite the dev team having to work just as hard to make all the new visuals and story parts.