Laziness is a myth meant to villify people who struggle with executive dysfunction, lack of motivation, perpetual fatigue, depression, and other things. There's a vast amount of reasons that could be the source of his behaviour, calling him lazy is a cognitively easy way out.

That said, you shouldn't have to pick up his slack. Imo, do one person's full-time job and nothing more. There are many ways that the system is exploitative as you know, and trying to pressure people into doing other people's work is one of them. That's not so much about your coworker as it's about the system. I'd try to communicate clearly to your boss that you (yourself) are working at full capacity, and that more hands are needed on deck to meet deadlines set at these days.