while i feel as if i largely understand what you're pointing out, i kinda want to offer my own speculation as a SWE who is very guilty in thinking in terms of sequence diagrams (and also more formal UML) -- sometimes UML is so fucking bogged down with (impl) details, i am just over here going "i don't give a shit about the (impl) details, i just want to know the abstract concept(s), and logical flows, and focus on necessary system interactions" -- bc i can (and should at this stage) worry about (impl) details later.

i prefer to reason about a system and component relationships using, say, a single word as representation, instead of glaring at one or many inheritance directionals, interface details, and other "field" information, which is usually conveyed in a UML node.

i do not think the lack of formalism is a degradation -- we work with abstractions after-all, so it makes sense to further leverage that fact and express things simply, at a high-level, and straight-forwardly -- you can pack a lot into a single word.

of course as the nature of any tool, there is a time and a place for its application. but i don't think it is fair to call it a degradation.