This line is so telling for why Morty felt like Planetina understood him like nobody else - after all, Morty himself is considered a product by Ricks. Also, Planetina's freedom was restricted by her kids' controlling behaviour and the fact that they could literally summon her at any time. No wonder Morty related to her.
I think he probably also related to her a lot in this moment as well - how often have people been freaked out by Rick and the impact he has on Morty's life?
Under the cut because this is more about the scene with Eddie than Morty relating to Planetina
It's easy to miss it because Morty spends most of the exchange angry and flips into attacking pretty quickly, but for a second he does look genuinely scared when Eddie is threatening him. He even tells him to stop. It makes me so sad for him because, no matter how badass and competent he becomes, he's still just a scared kid in these traumatising situations. I even wonder if he was reminded of the Mr Jellybean incident - trapped in a small space alone with a grown man trying to hurt him and without Rick to protect him.
I'm gonna cry, the way Beth holds her son and gives his head a little kiss, shushing him and saying it's okay, mommy's here. God I need more of Morty with his mom I'm so unwell.