Something I feel everyone is missing is that it doesn't seem to be just brokenness that makes you a Radiant but showing an outstanding virtue through that brokenness like Honesty, Honor, Leadership, and Bravery and loyalty.
and so far I think that everyone who is a radiant deserves it, Renarin for his loyalty, Shallan for her Honesty (or her ability to make others honest), Kaladin through his Honor, and Dalinar for his Leadership.
Shallan has shown that she can bring out the best in people by telling them how she sees them or how they could be seen, perhaps this has always been a quality of Shallan, as it has been said that shallan had a shardblade and a spren even before she lost her mother.
Something that was said that i can't quite recall where was that even with Radiant's spren, you have to show their virtue to attract them, just like any other spren. so maybe instead of finding all of the broken Characters in the books and pointing "Radiant!", and then discussing how broken they are, we should consider what we know of their character to judge it's possibility not exactly how broken we think they are.