Strong/weak is definitely another axis. I'm not sure they could never be strong developers. I'm not saying they couldn't generate code at all, just that the first couple approaches they write miss fundamental constraints causing the code to either not work or have horrendous properties, and they sort of jiggle their way into something that works. Sometimes the initial tries come from a Google result, sometimes they came up with it themselves, the important part is they don't fully understand the code in its context.

Anyway, regardless of whether they're really strong or not, the couple I've mentored have become tremendously valuable to my company, with performance outstripping my own (I think because of the higher tolerance to shitty repetitive frontend work).