They are considered that by whom? Not by me, they're not. Personally, I've never encountered a complex trigger hierarchy and I see no good reason why I ever would, and I write lots of triggers. But, that's just me. Your results may vary.
Evidently, even some experts do use triggers.
"I normally limit them to at most one per operation per TRIGGER"
Great! So do I! So far so good. I guess I'm still in the good graces of some experts.
"in full ANSI/ISO SQL, we do have schema level constraints, the CREATE ASSERTION statement, but that is another topic"
Not in PostgreSQL, we don't. Evidently some experts may not be perfect experts.