Many who originally set up a website at WordPress.com or who are considering WordPress increasingly are opting for platforms like Wix and SquareSpace - others that could be mentioned - that offer really polished and easy-to-use interfaces for average folk to build and maintain their own websites.
The WordPress theme vendor community could easily match such ease-of-use and reduced learning curve factors, IF WordPress CORE included the ability to easily disable/hide all standard menu options. Such functionality should also be extended to important screen items on various menus, in the core package.
Searching Ideas, I found a similar suggestion submitted last year. The moderator reply was that there are plugins to accomplish this. This functionality is fundamental and must be included in CORE, not reliant on hit-or-miss plugin support.
One possible implementation methodology would involve a single CSS file - evolving over time - where every key menu and screen item that can be toggled is listed in top-down nested order. Setting DISPLAY:NONE for a given item would disable it. If this file were given an AJAX interface, the same options could be over-ridden via UI toggles.
For every WordPress theme I've ever used, there have always been confusing redundancies and direct conflicts between menu and screen options associated with that theme, with plugins bundled to it or installed later, and CORE WordPress menu/ screen items. This isn't good. It adds a layer of complexity and confusion that's especially confounding to those not already familiar with WordPress.
I believe this Idea, if well implemented, would become the most important factor in helping WordPress stem the developing exodus to more-user-friendly platforms; allowing it to be much friendlier to newbies while, unlike the main canned platforms, also having unlimited bluesky roadmap potential.