I'm on a team that maintains two projects with over 500k PHP LOC apiece. They're built using a decent framework (Yii 1.x). One of them has a module that's about

I'm on a team that maintains two projects with over 500k PHP LOC apiece. They're built using a decent framework (Yii 1.x). One of them has a module that's about 25kLOC of AngularJS. They've each been running over a decade, and while there are some frustrations, it's not so bad. The biggest issue is lack of compatibility to migrate to later versions of the frameworks involved. They perform adequately for their purposes. These are business applications that are not designed to scale to huge audiences, although one does aggregate ludicrous amounts of sensor data. Both codebases interact with a lot of external systems via APIs and/or batched data transfers. When it comes time to integrate with a new/different backend system, it's not difficult. Could it all be implemented more elegantly in some other language? Sure. But in long-lived business tools, there's always an evolutionary process going on, and your pristine design from year two won't be useful with the changes they want in year seven. The ability to make fast changes is important. Lastly, none of this would be possible without functional and unit tests. Those are probably more important than the languages used. They're a pain in the ass to maintain as the business uses and functionality evolves, but it allows the refactors that keep the codebases sane.