Applications that use browser engines for rendering tend to be a bit sluggy compared to native applications, yes. But I don't think a common complaint is that a web browser as a standalone application is particularly slow either running or starting up. People tend to say stuff gets slow once they have a ton of tabs open, which makes sense.
Don't know how common it is, after all, people are used to all the slow stuff out there, maybe they don't even complaint when it's less frequent actions like opening a browser. Though at least for a ton of tabs, there are hibernating solutions, so very annoyed people can at least find a workaround, unlike with the unfixable startup delay
