I guess I'd say -- I think you're right that you shouldn't (ideally) be able to trigger true deadlocks/livelocks with just serializable transactions + an OLTP DBMS.

That doesn't mean it won't happen, of course. The people who write databases are just programmers, too. And you can certainly imagine a situation where you get two (or more) "ad-hoc" transactions that can't necessarily progress when serializable but can with read committed (ad-hoc in the sense of the paper here: https://cacm.acm.org/research-highlights/technical-perspecti...).