jgsugden
Legend
Your understanding seems flawed to me... they discuss the plane as part of the shape. More:I did google the definition, per websters: "one of two half spheres (see SPHERE entry 1 sense 2a) formed by a plane (see PLANE entry 1 sense 2a) through the sphere's center"
The plane forms it (in that the result of cutting a sphere with a plane that runs through the center of the sphere results in two hemispheres), but is not part of the hemisphere geometrically speaking. Notice it is defined as a "half sphere." It cannot be a "half sphere" with a bottom, at least that is my understanding. It has been too long since I had a math/geometric class, but my sons are taking linear algebra and calculus 2, I can pick their brains this afternoon.
http://mathcentral.uregina.ca/QQ/database/QQ.09.07/h/nicholas4.html
https://www.quora.com/What-is-the-formula-for-surface-area-of-hemisphere
Think about cubes, pyramids, icosahedrons, dodecahedrons, etc.... generally speaking, when you have a shape, you do not randomly cut into it and carve it out on one side.
You folks can question all you like... if you consider Sage Advice to be part of the game, your RAW Huts have floors. If you want to rule otherwise, you're ruling against Sage Advice. It really is not that complex.I also question your definition as they describe a sphere as "...nearly perfectly round..." Mathematically / geometrically it is a perfectly round shape.
By the way - they likely mentioned "nearly" in the definition as, to date, there are no perfect spheres (manmade or in nature).
Putting all that aside, I see this spell used all the time. I have never seen it be overpowered. I've seen it result in a TPK when the party hid in it and the bad guys collected all their allies to attack at once... I've seen PCs use this third level spell (cast without a spell slot, but still third level) to avoid 'wandering' beast encouters entirely. I've seen PCs run in and out of it during a combat to defend themselves, getting a benefit similar to blink.... none of it was overpowering.