Spotting has always been the Achilles heel of BoX, since day one. RoF has it better in some ways.
The most prominent issue seems to be the LOD transition causing problems. The shine on surfaces disappears abruptly after certain range turning the plane into a dark blob with less detail. This causes them to blend into the background thus practically invisible. Add to this the skin flicker aka chosen vs default skin alternating if looking away and then back.
Yesterday I was engaging ships in MP. I could see them in the distance just fine, but when I zoomed in to maximum they vanished! A slight zoom out and they appeared again. Same applies to ground targets, you can not see them from a 1km distance unless you zoom in.
Another thing affecting visibility is the strange smear/film/whatever on the cockpit glass. At certain lighting conditions it looks out right horrible, like a low resolution effect or banding. You see better if opening the cockpit than thru the glass. Also devs could remove the fingerprints, or whatever they are, on glass from all planes. Even back in WW2 the mechanics kept glass clean as seeing is crucial. And last, the scratches. Random lines drawn around the glazing, sigh. "The other game" makes this better and more like what I have seen during my career with planes, and counting.
Current visibility/rendering just causes a lot of frustration and forces people to use 3rd party programs or other gimmicks to gain at least some visibility. I really hope devs sit down and take a hard look in the issue as it is very annoying, detracting from the otherwise rather enjoyable gaming experience.