I’ve never thought the sims were as personality bland as some others do. They start off that way, but if you pay attention to their likes/dislikes and add aspiration and reward traits as you can, you can create some personality. Of course, if you play with autonomy off, you’ll never see that.
I have a sim (Morgyn, in my avatar) who absolutely hates the Cosplayers at GeekCon. That’s not something I set up for him. But, every time one of those costumed characters comes to sit with him at a table, he leaves for the karaoke bar across the street! I love that. Same sim loves thunderstorms (purchased trait), and when he goes out in a storm and gets hit by lightning, he loves it and gets energized. The game says it’s from the erratic trait, but he’s never had that trait. The reaction suits him, though. He loves the lost puppy movie, and hates the zombie movie. Keep in mind that this sim has a whole bunch of traits, beyond the starting three. I’ve played him for a while, and he has quite a few aspiration traits and reward traits, and I’m sure a quite a few hidden traits. One of the things the devs could do to give us more starting personality is to give us more starting trait slots. Three is not enough.