The issue with compare in PhotoLab is that every image is always shown in full quality processed from the RAW. To be able to do image compare a new image preview module would have to be built with just internal jpeg previews and with no ability to change any of the settings while in view mode.
My concern is that adding such a mode will just make PhotoLab more complicated and unwieldy. FastStone has some amazing four-up style tools. If PhotoLab could just copy that interface (select any number of images in image browser, right click to multi-file view where just zoom and hand work), multiview would be enough out of the way and simple enough.
Unfortunately the same band clamouring for multi image view won’t be content until multiview is three times more complicated than what is in Lightroom and still won’t be happy then.
Example: multiview simply cannot work smoothly with DeepPrime or DeepPrime XD for another two or three generations of GPU hardware.