Yes keep your mouth shut. I have the opposite problem of doing too much but people who get bothered about other people's laziness are my pet peeve. Unless you are a manager, managing people is not your responsibility. If you do well and offer your support to get them to where they need to be, you are doing your best, take the nice paycheck home and enjoy!
I have no idea what people are going through or what they bring to the team or what political crap is at play. If you are not managing people then you are getting paid for your labor, that's it. It is a manager's responsibility to evaluate what value their employees bring. Heck, maybe the lazy guy is there for morale! Lol. And if the manager doesn't care the he has his own manager. Maybe having X number of people in his team is good for politics and budget and so long as the guy isn't a liabilit he is left alone.
Do you want to be responsible for the guy offin'g himself after he quits, gets divorced, maybe wife is dealing with cancer? People are very messy, let people managers manage people and us techies focus our passions.