How do you speak about people who have left the company?

> the team lead would make it a point to trivialize anything the person who left had worked on

That guy ^ is a jerk. Also, you have to consider that in many areas, a lot of people know each other and talk to each other. So it's both morally and practically wrong to downplay somebody's work. And really, there's no reason to - one has to be a completely insecure ass to consider somebody else doing a good job being some kind of a threat to them. I'd say if anything, err on the side of more praise and recognition - after all, what the worst that could happen? They won't get promoted instead of you - they already left anyway! And if people see that you are willing to give credit when the credit is due - both your credit and your complaints, if it becomes necessary, will be take seriously.

In general, you want to work with & for the first sort of person (objectively recognizing contributions). Not the second (which suggests an immature worldview and narrow tribalism).

From my experience, most places have appreciated the work ex employees have done in the past, and have tended not to downplay their contributions. And that's how I speak about them too. Don't have anything bad to say about any previous colleagues.

Having grown up among assholes, I spent many years being surprised when people were kind.

Age has made me a fan of the no-asshole rule.