I agree, it would be better for them if they outgrow their brokenness on their own and they may very well do that before ever getting together romantically. Still, I don't believe that it is wrong for them to depend on each other too much, to make that relationship lead their lives. It isn't ideal but that's perfectly fine. We aren't, though I'm probably wrong about this when it comes to some people, here to read about idyllic characters. Kal and Shallan being broken can add spice to their relationship, make it interesting in ways that they might not be when they are "whole". It'll be interesting to explore that I believe.
It doesn't have to be a huge part of the story. It can remain in the background and it may not even remain a love triangle for long. The Adolin and Shallan "relationship" may end up breaking soon. Even if it doesn't BS is not required to spend much time on it.
It'll definitely be a source of conflict but it isn't insurmountable.