Well, scales are often unrealistic. It's very common to see game characters that are as tall as a tree, and sometimes even as tall as a town or only half of the size of a castle (Dragon Warrior, Final Fantasy !)
Also, what compression method to use really depends on how you want the game to be. Celius's platformer seems to really need to work with screens, as the game has been designed that way. All white areas don't have to be encoded as long as the scrolling engine doesn't allow scrolling when a screen isn't present in that direction. In the case where screens always scroll only one direction, this even allow clever switching to horizontal and vertical mirroring so that you can always write big blocks of data to nametables without worriying about a row/column format and without having glitches. However, this won't work if scrolling to both directions is needed at the same time.
Eventually, having bigger maps often also mean bigger metatiles and then, your decompressed map takes less space since the metatiles are enormous, and you only need to keep track of the metatiles, not lower units. After all it doesn't seem that hard to random-acess a RLE map, so yeah, if it's possible to do it without having it to RAM then do it. Personally I like the RAM approach as the map is "modifiable", but I'll admit I've never made code that modify a map like that in my game yet (but I plan to do it). It's also good with object that interact with their background. For example if you want an enemy who is a statue, and when the player approaches it the statue starts to move and attack him. If you do only a sprite approach, when the statue will be scrolled in screen, it will most likely be viewable that it's made of sprites, and the player won't be tricked (especially in my game, where a whole map is scrolled at a time without any care to sprites before it's fully scrolled), so that's not a good approach. However, if you made it BG, and then have the object replace the statue graphics by some other metatile, but then create its own statue sprite, everything will be fine. You then need RAM so that when the player open the menu and close it, you know if you what metatile to draw, that can be a different one than the original when the map was loaded.