I think this is a pure optimization power gamer take.
Few Rogues or Monks are Mental stat primary. That defeats the point of being one.
To make sure you are tracking what I said; my statement was most Monks and Rogues have it as their highest
or second highest stat. So primary stat or secondary stat.
I would agree most Monks do not use Wisdom as their first highest and most Rogues that are not purposely building for maximum damage do not use a mental stat (usually Charisma) first. But a mental stat is typically second for both of those classes.
Most Monk abilities key off of Wisdom and Wisdom boosts their AC. Wisdom is almost always the highest or second highest stat. While I have seen low/mediocre Wisdom Monks, I have seen far more with it as the highest stat than with the 3rd highest.
Mental stats, particularly Charisma, work very well on a Rogue due to the large number of skills they get as well as Expertise and Reliable talent. After Dexterity there is no better stat that fits with the "point of playing one". If you are playing a cliche stereotype fantasy Rogue then from a thematic point of view you could pick Intelligence over Charisma, and I have seen that done for that reason, but Strength and Constitution is really a corner case uncommon type of build.
Under the 2014 rules Constitution was prevalent as a secondary stat for Rogue optimizers in combat-focused games, but it isn't any more because of the extra damage and damage type versatility a Rogue gets off of Truestrike. Being able to do an at-will Radiant damage sneak attack with extra damage to boot at range or in melee is extremely effective. This is a game changer right from low level when facing Zombies like almost all campaigns do.
Note I am talking here I am talking about single classed Characters. Multiclassing changes a lot of this.