Obviously, you would hope that you can have several Level 1, a few less L2, and some sort of top level escalation, to either engineering, partner services, or something. But the other factors are time, and leverage. Having a good escalation process means you can have someone to take escalated tickets, architect a solution, and de-escalate. In this way, everyone learns, the highest level is able to focus on more challenging issues, and the issue get solved.
Escalation resource should be good delegators and must have enough bandwidth to work on what are likely more complex tasks.