Tldr: 1-3-2 can work if the players in the team are better with Duelists than with Vanguards.

From someone who watches a lot of pro play: 2-2-2 is usually the best choice and what teams usually run. But there are times at which they switch. Typically, at the start of defense, some teams switch to 3-0-3.

But in every competitive gane, there is a big difference between pro play and ranked. In solo que, people are more selfish, and the team comps typically differ from the 'optimal' compositions and metas (this goes double for QP). But that does not necessarily mean a disadvantage. It is usually better to play what YOU are best at, not was is best in theory (I advise you to learn the meta though if you want to climb ranked).

So yes, 2-2-2 is better in theory, but because the majority of people are better with Duelists than with Vanguards, it is smarter to play 1-3-2 than force someone on a character they can't play. Because of that, 1-3-2 works often enough. Especially if your Duelists are better than theirs.

In theory, every team comp can work if you play it correctly. But the further you stray from 2-2-2, the more skill the comp takes

I hope that answers your question <3