as a workaround for pickups, have you tried scaling down with mitchell filter (bicubic) so you get a softer downscale with less pixelization?
yeah it will definately go blurry. problem is that if the engine was cutting the size of your key or hp1 in half, it is still downsampled. you can't make something smaller without losing some detail.
one thing i have been playing with is using esrgan AI upscaling, then downscaling the upscaled image. depending on the ai training model that may or may not look good with your handrawn pencil aesthetic. check out n00mkrad's cupscale and his models