There are probably a dozen bearings in your motor that use synthetic cages. Almost every bearing in your transmission uses PA66 cages. There is nothing wrong with it, and in fact it can be preferred for certain situations. There are a lot of benefits with synthetic cages.

Just because a bearing uses a non-metal cage is no indication as to how good it is. I can give you a dozen stamped cage ball bearings that I wouldn't trust to run a pencil sharpener.

 

I'll agree there are plenty of all metal bearings that aren't so great, too. Might be some quality plastic cage bearings, but the ones I trashed looked awful flimsy, and the bearings didn't even have any i.d. numbers on them, cheap stuff. I've seen cages mangled in both plastic and metal, just have to look at what you have and make a decision. I guess what it boils down to is I want the sturdiest construction I can get in wheel bearings, consider those the most critical bearings on the bike. And I'm an old guy, hell, I miss kickstarters.