There's an option to force 2x, which is what i use. My screen is slightly too short, resulting in the bottom scroll bar being out of reach, but i can get around that with my computer's multi-touch capabilities. (The arrow keys work, too.)
I've encountered the black spots issue too. Entering and exiting playtest gets rid of most of it for me, but i don't know how effective that is on 1x.
There's even a few glitch tiles that can be clicked on, which I don't think should be a thing at all!
I don't see why that would be a reason for you to not use the editor. It's not like they get in the way when you're trying to click something else.
Something that does bother me that hasn't been mentioned here is that selecting a tile and moving the mouse to the editing window to place it sometimes results in a click-and-drag. The damage is usually fixable (still annoying though), but sometimes it isn't because the undo button can glitch and stop working for reasons unknown to me, and that has resulted in loss of progress on at least one occasion.