There's a difference between every attraction being an E-ticket and every land being properly themed. This has nothing to do with the scale of the addition, and everything to do with the execution of it. I'm not sure what you mean by MK lands failing to live up to your mythical E-Level Land standards. For the most part, the existing lands throughout WDW are pretty consistent in execution; the detailing of Adventureland, the UK pavilion, and Sunset Blvd are all about the same level.
For attractions, it's good to have a variety of types in order to fill out the parkgoing experience. It's similar to a restaurant menu, where there are all types of dishes of varying size and price, but the execution of the dishes is expected to be uniform across the board. Just because something isn't the headliner doesn't mean that it should be exempted from quality standards.
To prove that the quality of a themed area isn't directly linked to the attractions in it, let's consider the Morocco pavilion at Epcot. It has no attractions, but a top-notch attention to detail. It's a pleasant place to explore and absorb details, wandering through hidden passages with surprises around every corner. People seem to genuinely enjoy discovering what's there, and I often see groups lingering in quiet corners. Are there occasional visual intrusions poking up above the horizon? Sure, but they're no more distracting than the swarms of tourists or Disney-branded trash cans.
Now consider the Backlot area of Walt Disney Studios Parc. It contains a headliner stunt show, D/E-ticket rollercoaster, and a C/D-ticket walkthrough show, but almost no theming to speak of. The main walkway is flat asphalt with plain warehouse-type buildings on either side; the only decorations are the oversized marquees that attempt to hide the industrial structures. It's such an unpleasant environment that it's difficult to find photos online that show the whole area; nobody lingers here any longer than necessary. There are no real visual intrusions, because there's no attempt to define what does and doesn't belong in this environment
Which of these has headliner attractions? Which of these is a pleasant environment that's worth the price of admission? Just because attractions aren't headliners doesn't mean that the themed environment doesn't need to be up to par