But you need to know they exist. :)
I would be very surprised if any enterprise of significant size and IT complexity didn't have an IT incident response team. I'm biased but I think they are a necessity in complex environments where oncall engineers can't possibly even keep track of all their integrators and integrators' integrators, etc. It also helps to have incident commanders who do that job multiple times a week instead of a few times a decade.
I can go to a website and type in search terms, URLs and pull up exactly who to contact. Even our generic "help something is broken" group relies on this. There are many names listed so even if the on call person listed is "making dinner", you have their backup, their manager, etc.
I can tag my system as dependent on another and if they have issues I get alerted.
Escalation teams are usually reserved for the "oh fuck" situations, like "I don't work on this site but I found it broken" or "hey I think we are going to lose soon this availability zone" or "I am panicking and have no idea how to manage this incident, please help me".
They're a glue mechanism to prevent silos and paralysis during an event, usually pretty good engineers too.
If you didn't know what it was, you could page the SRE team and we'd diagnose with you.
Sometimes as SREs we would shortcut the process and just know who the right person is with the answer, but at least this way that tribal knowledge was somewhat encoded.
Would be nice if there was better tooling for going from observed problem to responsible team.