I can agree that they also face pressure. But on the one hand they have more options, for example putting the work onto a lower level guy, they get less bad feedback for doing bad work (e.g. nobody analysis how stressed his workers are, but the developers code gets analysed for code quality, unit test success, peer reviews).
The last point I put separate because I think that one might actually be just subjective. In my eyes it seems, as if they also have less work on their table, really. Example: There are a lot of things a product manager should do. For instance, he should learn to know the customer. But at least where I worked until now no product manager was asked by his manager how much time he spent with customers. So no product manager spent a single second with a customer. Also a product manager is in my eyes responsible that the user interface is translated correctly. He can pay an external office or convince some engineers to do it who have that other language in their repertoire. But when he constantly hears from the engineers that the three or four languages we can evaluate are so shitty that nobody can even closely know what the corresponding text says, then he should review his translation workflow. Never seen that either. The only situation in which a product managers needs to hussle is when the sales department that actually talks to the customer has a problem they can't communicate directly to engineering because both worlds speak different languages. And the only reason the prod manager needs to get active is because if the stress gets out of these two departments his boss needs to do work and then his boss will be angry. So in these situations he really has a lot of stress, because it's hard to convince engineering of some of the requests that come from sales, but sales needs some kind of results to make the customers happy. But this situation only happens in one of 5 feature or bug requests. Therefore I think the engineers have more stress. They have stress with all 5 requests, all the time. When they finish one, there are already the next three waiting. And in this one request that required prod manager intervention the final result that should be implemented is often so bad that this one is even more stress than the others.
To summarize, yes there is manager stress as well, but it's not as much. And if you get 120% of the pay of another coworker or more, I think it should be okay if you even have a little more stress. Therefore people working on the corresponding lowest level seldom have tolerance for the "hard life" of the manager.