Workplace Daily Life

Lately, I've been thinking a lot. How does the company view my full-time job and my part-time job? I know they hire part-timers because they're short-staffed. So, shouldn't part-timers help full-timers with their workload? But my company just hires part-timers to collect a salary. Is that reasonable? Mainly because whenever I'm at work, it's almost always just feeding milk, and very slowly at that. Others might have finished feeding two babies, while he's still holding the first one. After feeding, he rarely helps with other tasks. He's either scrolling on his phone or sleeping. This leaves the full-timers incredibly busy. And he gets paid a daily wage that's much higher than the full-timers'. Sometimes when I see this, I really wonder if this world is sick.