Heck, I'm generally a platoon advantage guy. I think LH pitching has been tough for every LH hitter in the history of baseball.
But...even if one believes that, taking Julien out for a dubious RH hitter that early just about guarantees Margot is getting 1 or 2 ABs later giving up the platoon advantage.
Maybe Julien wont hit LH pitching, ever. But I'm pretty confident Julien against RH pitching is a better hitter than Margot against a lefty.
Don't do it.