Hi there. I often read the forum but don't participate actively much. I have got this idea that I haven't seen addressed anywhere yet.
It seems that post-recreance radiants must be "broken" in order to bond a spren. For Kaladin and Shallan this has been explicitly described. Dalinar, Renarin and Lift all have issues. Adolin is being set up as well at the end of WoR. This echoes the way that Kelsier can talk to Spook in Secret Histories.
Before the recreance there were a huge number of radiants and it seems weird for me that every single one of them had to have fissures in his/her soul to allow bonding. Also think about Dalinar's vision in which a KR offers him a position in one of the orders. The offer is only contingent Dalinar's ability with natural implements but doesn't mention being broken inside.
I suspect that, in normal times, a broken soul is required for bonding (this would make it extremely difficult to produce surgebinders) and that the oathpact is somehow related to a "deal" in which radiants are easier to make because no broken soul is required.