256x192 used to be a very good resolution, but often the screen is not truly bitmapped. Instead it is made up of characters from ROM or RAM. I believe most 8-bit computers has a limitation at 256 characters in a set, sometimes less than that. In that case, each character code can only be displayed once on screen, in a matrix like this:
@ABCDEFGHIJKL
MNOPQRSTUVW
XYZ[£]^ etc
You would define a custom character set of 256 definitions, in which you address individual dots based on where on the screen each character is located as above. If each character occupies 8x8 pixels, you can get a bitmapped area at most 16x16 characters = 128x128 pixels, which is much less than 256x192.
Some computers (e.g. the VIC-20) have special character modes where each character uses 8x16 pixels. In that case you could in theory get 32x8 double height characters = 256x128 pixels. In particularly the case of the VIC, it can not display that screen width but can nicely display e.g. 25x10 double height = 200x160 pixels.
I don't know how flexible the Panasonic computer is, but I believe it works with custom character sets as described above. A lot of the area is blank or filled with one colour, so one and the same character definition could be used many times, and only use unique characters for the detailed graphics.
I suppose the initial reason behind making loading screens is to give the user something to look at while loading, and to let him or her know progress is under way. Often the system loading routine is very bland. When you mention 2048 Kb, is that kilobit? 2048 kilobit equals 256 kilobyte, which is a lot even for CPC6128. Perhaps you mean 2048 bytes = 2 kilobyte?
I am of the old-school who uses SI units: k, M, G instead of Ki, Mi, Gi and also differentiates between lower-case b as in bit from upper-case B as in byte. A lot of people unfortunately don't adhere to this nomenclature, which makes it a bit fun everytime one speaks about millibit (mb). The same people tend to write kilo with capital K as in KHz or even Khz, when it really should be kHz.