It's funny how often people say "it's just habit / muscle memory / etc." in response to these kinds of discussions, as though it were somehow a counter-argument, and not something that corroborates the argument against making sudden, drastic UI changes.
It's really weird how common it is for people to say "well, Y is only true because of X" in response to "Z doesn't work because of Y", and thinking they're somehow defeating the argument against Z. If you acknowledge that X exists and causes Y, and accept that Y isn't compatible with Z, then you are conceding that Z does not hold!
And that experience is determined as much by the users' own expectations and prior experiences -- yes, including habits and muscle memory -- as any quality of the interface or the design of the software.
It's not merely a matter of optimizing the new-user experience for your own particualy software, either, as new users to your software will still be bringing with them the expectations and habits they've acquired through experience with other software. We're not in the '70s anymore, with new users likely never having used any software before, and where you're starting from a clean slate. People today have lots of particular expectations of software, informed by conventions evolved over decades and their own years of experience.
Also, clutter…
These are measurable things, not moody things.