I was trying to delineate between large applications and not-so-large. Larger applications are more demanding in terms of language and software engineering discipline. Small applications can generally be written reliably in any language, even JS, PHP, and Perl!!! (Sorry, I couldn’t resist. ;-)
Yes, LOC is a fairly arbitrary metric of complexity. It’s the only one, however, that is widely accepted…for better or worse. Some have attempted to replace this metric (for example, Caper Jones), but LOC has stuck. It’s not entirely accurate, but it’s not entirely wrong, either.
“Lives affected” or “dollars generated” would not be applicable to the question of what constitutes serious software engineering.