Because he had a better sales pitch on JP server.

Lid got like one or two DVs to show her prowess and advantage. She was good for DV, but she was not essential for trials. So, it's okay if you don't have her or would be nice if you have her. Older breakers can do the work (DV or some trials), just not as good.

But Vaan? He got a whole trial favoring him and his TMR/STMR. That was JP Behemoth K. His high full-break suits this trial more than other breakers due to 30% break resist and frequent dispel (either from your party or from Behemoth itself).

Then his TMR and STMR with high physical evasion are very useful for this trial because the physical damage load to party is very high (Do note: GL has better evade gear). Either use 50% gen mit 70% phy mit def buff, or go full evade, or wait for NV meta/some sick GLEX units.

In short, getting him would make this trial easier. Also, less reset.

^{yeah, most players would need a guide for the trial and a guide to change the RNG seed}

So, what happened after this trial?

Vaan doesn't become bad at all. He stays at the top but no longer alone.
The other breakers (Lid, Rikku, Machina, Vanille etc) become as effective as him for trials without the break resist thing.

So, should you pull?

No, I don't do that kind of thread. Just pull if you need him or like his kit/TMR/STMR. Don't sell your kidney or child to pull him though.

Personally, I kinda want either Lid or Vaan.
Never get Lid on JP, and got Vaan just a few hours after I got NV Fid.