It's an unfortunate truth that many rack manufacturers don't give any thought to the ease of fitting lights. Blackburn racks, for example, have nothing to fit a light to.
I now have a rack which I don't much like in some respects, but is good enough, and has a bar with holes in at the back to which I can fit lights or light brackets. If all racks had such a bar, I expect that more light manufacturers would make lights or brackets to fit it. Cateye does.
AFAIK, reviewers rarely criticise racks for not having light mountings, or praise those that have them. That annoys me.
I think the plates are relatively standard (there are two horizontal hole spacings, & the traditional two vertical holes as in the old reflector bracket), but many manufacturers don't provide any plate at all, or anywhere to fit one.