I don't think it's as misguided or harmful as Schreier suggests. When people refer to the game engine, they refer to the toolset used to build the game, features like the renderer, the lighting engine, and systems that handle he games physics.
From an outside perspective there's never going to be a single, key issue that we can identify as the cause of the problem. If it's the renderer that's causing slow load times, as opposed to the lighting system, then an outsider has no real way of determining that. At least from my perspective, it's fine to refer to the 'engine' in a broad sense.
Additionally, in Fallout's case, Bethesda's games have suffered the same problems for years. It's not just a single, isolated game that suffers the same problems, therefore its logical that people point fingers at the tools used to build each game, rather than qualities of the individual title.
Of course, to say Fallout 4 and Fallout 76 use the same engine, isn't strictly true. However, it's hard to argue against the idea that the engine is the cause of its problems, rather than the explicit features of the game design, or how it's coded. Blaming the engine is actually a pleasant alternative to blaming the explicit implementation. Saying it's an engine problem is more pleasant than pointing fingers at the gameplay programmers, for instance.