Have you tried exporting your sequence to see if it’s just playback or if it does affect your final output?
It could depend on your display settings, how close you are sitting to the screen, sequence settings….
PNG and TIFF work for me. I try to have the graphics made at the same frame size and 72dpi is fine if the graphics don’t need to be resized. 150 dpi is usually plenty if I do need to resize.
good luck