Rúguǒ shuō tā yǒu shénme quēdiǎn, nà jiùshì tài gùzhí le.
If he has any flaw, it's that he's too stubborn.
Tips
grammar
如果说 is used to set up a contrast or comparison, almost always followed by 那/那么 in the second clause. The pattern 如果说 A,那么 B creates a rhetorical 'if...then...' structure that sounds more nuanced and deliberate than plain 如果.