How much of it is due to Agile (which is a very broad concept even though some people mistakenly equate it with scrum), and how much is it due to corporate pressures and inadequate processes though?

I find Agile conceptually meshes a lot better with “standard” product and solutions development thanks to the tighter feedback loops and increased reliance on local expertise over centralized planning. This only gets truer as project complexity grows.

However some companies try to make Agile work with top-down decision making and/or hard deadlines, which are deadly antipatterns. As for lack of time/resources and/or timesheet micro-management, this isn’t a problem unique to Agile nor something that waterfall is exempt from.

Good agile teams are mostly independent and can define their own testing/release cycle as required for a given project; though of course when that happens there are at least a couple layers of management who feel a burning itch to stuff their dirty nosed where they don’t belong because if the team succeeds despite their lack of direct involvement then everyone might realize the emperor has no pants.