Or is this another case of the internet being, well, itself?
PF2E "suffers" from being well balanced and also "suffers" from being too easy to keep viable to play all the way up the level ladder. It also "suffers" by letting any character of any class be able to fun and engaging and lastly it "suffers" from it being somewhat difficult to make a too weak or too powerful character for all but the most extremely savvy players. As in... you probably have to be really hyper aware of the game and all it's angles to make a bad character (unless you go for Investigator).
As a result of this... OK sure... Casters can be 'unfun' if what you're seeking is to be the person who by 5th level is single handedly doing 50% of the group's entire damage, while also being unkillable, AND having all the out of combat explorable and social options.
If your idea of "fun" is to be the locked in by design main character - then casters suck.
Because unfortunately, the game gives everyone room to shine, but even more unfortunately, the game shines best when everyone works together and tried hard to NOT hog the spotlight.
It's a very bad game in this way - letting everyone have fun is just... why... why would you do that?
Personally I'm weird. I absolutely love that anyone at the table has about equal opportunity to shine and be an amazing team player. I love that no one dominates.
I've been away from gaming for almost 20 years, and the last time I played I was playing the "powerful class". It was from some random d20 book and was an archer that basically had unlimited fireballs that looked like a rain of arrows. I think whoever wrote that book went on to design the World of Warcraft Marksmanship Hunter because it was basically that. In D&D back in the day (and I hear still today but cannot verify) - that result is usually the Wizard about 2 levels higher than we were. The idea of balance there was that for the first few levels the Wizard was super weak, but by mid-levels they were so powerful DMs couldn't find anything in the book that could present a challenge...
I love that in PF2E - my Witch or Druid or Wizard will never be that. At low levels I am not too weak, and high levels I am not too strong. Somebody who worked on writing this game read up on Goldilocks... We all get to be 'just right'.
And it's still fun as heck. The Casters all have so much variety to them that even two Witches or Two Wizards could be played on the same party and feel like completely different classes. The same goes for two back to back Fighters or back to back Rangers or... well... anything except an Investigator. The game has one fail... and that's it. The Investigator. A weird gimmick that means you will be either S-tier or F-tier depending on whether or not your GM's idea of a 'detective / police drama' is 'Hercule Poirot' or 'COPs'. And if it's neither, you won't even make it to F-tier... But for a game with that many choices to only have one miss is pretty amazing.