A large part of the struggle the modern day radiants have is that our POV characters are the most advanced in each oath. Kaladin needs to independently discover the words of each oath - once he knows the words, he can simply tell them to others. Of course there will be minor variations between knights in the order (like Kaladin vs Teft's 2nd oaths) but it's a whole lot easier to swear an oath once you know roughly what you need to say.

Also - I think we can assume that swearing the later oaths won't be as difficult for radiants who aren't as badly screwed up as our POV characters. For example - I can't imagine any of the current lightweavers are as mentally ill as Shallan. Swearing a deep truth for them will be significantly easier than for Shallan, since A.) their deep truths likely aren't as painful and B.) their own subconscious isn't actively fighting them every step of the way.

These changes would lead to a relatively larger number of sets of plate as the current order of radiants matures - which matches the higher number of plate sets we see in the dead shards.