Shortboard's close synonyms are shortcomings, weaknesses, frailties, inadequacies, deficiencies, and weaknesses, among others.
Short board itself is interpreted as something that is inadequate, incomplete. Personally, I think one of the most similar words to shortcomings are shortcomings, weaknesses, deficiencies and inadequacies.
While weaknesses and weaknesses can also be taken as close synonyms for shortcomings, these two words are slightly more emotional. For example, singing and dancing are my weaknesses. In this sentence, we can replace "shortcomings" with shortcomings and weaknesses, but not with weaknesses. On the contrary, we often use the phrase: Someone is someone's weakness. We put the soft underbelly here is very appropriate, if the sentence will be "soft underbelly" replaced by "short board" but all of a sudden become twisted up.