Seems to me that Kaladin is better in the sky, (windspren seem to worship him), and Szeth is better at killing.
Kaladin could have played arial rugby better and got the gem to his holiness quicker.
And Szeth versus Amaram.... he could have nightblood slashed Amaram easily, being perhaps the best overall fighter in the series other than Dalinar. Heck, he can take a nick from Amaram in exchange for a nick with Nightblood, which will consume the most hated man AND permanently end the main powerhouse unmade. It might take a few minutes but nightblood is that awesome and will eat the unmade (IMO, no resurrection possible)
It makes sense that the tasks were assigned this. This is a what if conjecture.
(Warbringer spoiler but very minimal if you’ve read Oathbringer)
It started when I was thinking of how powerful nightblood is. It consumed a full stormlight charge in seconds. In Warbringer, it may have consumed hundreds of thousands of invested soul fragments, and it was consuming those in alarming rates too. So if you imagine if the consumed power adds to the size of its spren, it may dwarf the unmade in size and may be closer to stormfather. Hence I believe if it was used more fully in Oathbringer, it could have devastated Odium’s forces. It is the only confirmed way to end the Fused as well.
PS, first post but read all Brandon’s books twice at least.