I had the idea to play a two-weapon PF2e Rogue character wielding what I considered to be the classic two-weapon combination: a rapier and a main-gauche. Then I discovered that the main-gauche is not available to a rogue by default, which surprised me. Then I spent a lot of time searching The Internets for reasons why the Rogue class should not be able to wield a main-gauche in PF2e without expending extra feats to do so, but so far I have found nothing. So...is there a game balance reason why the Rogue doesn't have the main-gauche available in PF2e as a class weapon by default?
Then I'm confused why parrying with a main-gauche should trigger an attack of opportunity. I mean, my character is already holding a rapier and a main-gauche, makes a first attack with the rapier, and a second attack with the main-gauche, then wants to use the main-gauche to parry attacks until her next turn. What is it about parrying with an already-in-hand main-gauche that causes it to draw an attack of opportunity?
In the end, I know I could use a dagger as the second weapon for the same agile trait and damage as the main-gauche, but I would lose the parrying trait. I find it hard to believe the main-gauche is mechanically unbalanced. I am just curious if there are rules-balancing reasons for this particular combination of rules (before I throw out the whole character design).
TIA for any insight you can provide :-)
EDIT: One last question: I know the rogue can take Weapon Proficiency general feat to become "trained" in martial weapons (so I could use the main-gauche at the Trained level), but I am unsure how I promote that skill level to Expert, Master, etc., since the main-gauche is not in the list of Rogue weapons that can be promoted with Weapon Tricks?