Software written in a simpler language like Objective-C - verbose, fast to grok and fast to compile is actually more maintainable in the long run than a so-called "developer friendly", humongous, complex and slow-compilation language like Swift.
A lean language reduces the surface area for beautiful expressiveness by clever people - making sure the dumb/junior guy who is maintaining your project in the future can actually fully understand what is written. And it can build and run fast - so you can iterate and test out software behaviors fast.
No one in this world is immortal. If it takes too much time to grok code, write/compile/run tests - a developer will be disincentivized to do so, no matter how amazing the language features are.
My guess is that Swift has adversely affected Apple's overall software quality. As more software moved from Objective-C to Swift, quality has dropped precipitously.
It's easier to read and navigate a well-written Swift codebase than a well-written Objective-C codebase
Conversely, it's easier to debug an Objective-C app than a Swift app, simply because compiling and debugging is so much faster, and debugging so much more reliable
I don't know about a software quality drop being attributable to the migration to Swift. So many other things have also happened in that time — much more software that Apple produces is heavily reliant on network services, which they are not very good at. I find Apple's local-first software to be excellent (Final Cut Pro X, Logic, Keynote) and their network-first software is hit-or-miss
They have also saddled developers with a ton of APIs for working with their online services. Try to write correct and resilient application code that deals with files in iCloud? It's harder than it was to write an application that dealt with only local files a decade ago!
Swift is easy to blame, but I don't think it's responsible for poor software. Complexity is responsible for poor software, and we have so much more of that now days
There's a limit to how "lean" a safe, low-level language can be. Rust is leaner and simpler than Swift but not by much, and pretty much all of its outward features are "load bearing" to a far greater extent than Swift's.
(People have tried to come up with simpler languages that still preserve safety and low-level power, like Austral - but that simplicity comes at the cost of existing intuition for most devs.)
A lean language reduces the surface area for beautiful expressiveness by clever people - making sure the dumb/junior guy who is maintaining your project in the future can actually fully understand what is written. And it can build and run fast - so you can iterate and test out software behaviors fast.
No one in this world is immortal. If it takes too much time to grok code, write/compile/run tests - a developer will be disincentivized to do so, no matter how amazing the language features are.
My guess is that Swift has adversely affected Apple's overall software quality. As more software moved from Objective-C to Swift, quality has dropped precipitously.