There will be a much bigger difference due to all the display variations out there than the actual compression, so I believe artists are out of luck here. No matter what they do it will look different on different screens.
In the end, what is more important, being able to add twice as many animation frames and having more and smoother animations, or possibly risk some color variations because of compression, that 3 people somewhere may or may not notice.
We do the same with audio in Construct. It is compressed, so why not graphics? Some people care more about audio actually ( I care at least as much ).
Ideally ( if possible ) give people options, from what's currently in Construct to more severe compression.