It is always far harder to get a significant pay rise at the same role than through promotion or changing employer. Even promotion rises tend to be smaller so is worth negotiating.
Moreover, experience is one thing but when a new candidate is hired there is always a ramp up period as they learn the ropes, and the more senior the position then generally the longer this takes to see maximal performance. Yet the employer has to pay the salary of someone just learning everything.
In my limited experience the more senior the less time you get. You're expected (within reason) to hit the ground running. Also in my limited experience the more senior and experienced people themselves want to set the tone and establish their authority almost immediately.
I think our most recent most senior hire, at their first dept meeting presented fairly detailed work agenda for the coming months.