I had wondered about that quote as well, but I've never been able to make all the pieces fit.
It does seem to strongly imply that Heleran at least had some Radiant abilities if he could have "trained" Shallan (plus the mention that he'd joined the skybreakers), but if he'd bonded a spren enough to have a blade, how did his blade stay after he died, like his shards, since unless he'd broken his oath, the spren/blade should have been fine. And if he really was proto-radiant, he shouldn't have been able to handle a common "dead spren" shardblade due to the screaming. I guess there's nothing saying it's impossible to handle one, but it seems like it'd be very problematic and I have a hard time seeing a spren that he was partially bonded with being okay with that. (although, Renarin....) Not to mention, whatever abilities he'd gained must not have done him much good in battle, since, you know, death by common spearman and all.
So possibly he had an honor blade?? (that Amaram has now?? Scary....) or Nalan has some other way of training his followers?? Or can you "join the skybreakers" or at least Nalan's current corrupted version without having any abilities at all and you just do what you're told in the name of justice?
I feel like I'm missing some piece of something somewhere.
