So when it comes to the reputation it has among console gamers as being poorly-performing, is it because all of the developers behind these games are inexperienced?
Couldn't it be that there are issues beyond widespread user error? Surely there's more to this than "all those devs are bad", after all, even if it's an issue of communication.
There is a certain style of developing games in Unity, that Unity encourage because it's the friendly-easy way to use Unity for small and novice developers, that is totally inefficient at scale. Unity is a deep and multi-faceted beast with many features, not all of which are well documented from a low-level standpoint. A studio new to Unity can easily be led down a road of thinking "well I just drag in this mesh and it works!", which it does, but it probably doesn't have the right import settings, it might have a mess of transforms when instantiated, and so on.
I guess what I'm saying is that Unity is really good and easy to get into for "high-level" game development where you can drag and drop stuff, and it kind of works, but low-level Unity development, and Unity's recommend practices for that can be remarkably different. You have to pay just as much attention to things like vertex budgets, draw calls, occlusion, and all that jazz as you would in any other game.
There are also hidden traps that are easy to fall into. For example, the foreach syntax in C# should
not be used during update loops because it allocates memory, causing frequent garbage collection spikes. Also using things like Linq extensively is a bad idea too, despite its convenience.
I can't remember if this is the case any more, but using the Update() method on Unity MonoBehaviours has a hidden cost. So in complex scenes with lots of GameObjects, that cost could become substantial. In that case it's actually much better to write and manage your own Update hierarchy (which I'd argue should be done anyway, but that's another topic).
Unity's like a Swiss Army Knife in that it's really flexible, but it's easy to cut yourself on it.