I took an organization that couldn't put out two releases a year to one that put out once a month, and the owner/manager complained bitterly and pushed new features into the discussion ON THE DAY OF RELEASE.
2nd level management had to constantly, repeatedly attest to the good that the tempo and structure brought to the organization and customers.
My entire experience has been: good management + talented developers = success, and bad management or untalented developers and it fails, but it really has nothing to do with the methodology in play. I've seen (and been part of) hard core agile teams burning to the ground, and teams with no methodology be wildly successful. (And vice versa)
Agile bothers me because it generally aims to commoditize developers, and yet the best places and teams I've worked on always were they opposite: it was about finding the best way for each individual to work, and designing processes around the rhythms around whatever industry they were working in, rather than assuming everything should fit into 2 week sprints.
The best places to work adapt the process to the team.
The worst enforce a process on the team because it makes managing them easier.
The number of workplaces I've been in who equate the number of hours that people are in the office with their productivity, because managers could measure attendance easily, and had no idea how to measure actual productivity...
Still, a lack of a strict methodology doesn't necessarily make it waterfall.
Then, that whole steaming pile was thrown over the fence to QA which tried to figure out heads from tails and developers started fixing the issues they already knew about but had to leave in so that they would make their deadline.
THEN came user acceptance testing, where people actually looked at the product at the first time. This is when people realized what the miscommunications 6-12 months ago, and the change request process started.
Finally, over budget and after everyone was finally exhausted and tired of fighting, it was released to users with promises of changes after the release.
From this world, SCRUM and the manifesto makes sense.
Within those projects, waterfall was completely removed from the numerous tasks needed to get the project done so the developers never saw it.
Getting waterfall involved at the project level tasks day today has a lot of issues though. It can run a lot smoother if your team has a low expectation of pivoting due to new projects or production support needs.
It’s not without possibilities, but a lot depends on how far removed it is from day to day.
Modern waterfall where you have documentation in git with references into tests is 10x better than the waterfall of old.
As far as I can tell "agile" mostly is about predictability, not about efficiency. Most of the places I've worked, when we switched to agile, the efficiency of the team got worse, but management was generally happy because they felt like they had much more control.