Seems pretty normal from two Bay Area startups and two FAANG-sized orgs. Primary should respond, secondary shouldn't be disturbed unless primary seems incapacitated (no pager ack) or is at wits' end.
Edit: I should add that the secondary gets paged more often while the primary is new to the team and doesn't know how to fix everything. In return, you go on call 1/n less often in the future.
If I need to sleep in after a bad night, it's always been fine.
My current job does this, they expect you to respond to pages at 4am
You're telling me this isn't a thing other places?