i dont understand why salaries should be same for a similar role. If I work twice as fast and with a better work quality than my collegue why shouldn't i get double his salary? are we in a communist country?
Job title makes it clear that it's about greater responsibilities.
"Why is Jeff paid more than me"
"Because Jeff is senior dev and you're junior dev" is a much easier conversation to have, and everybody's job title is very visible.