Lots of open source software uses arcane concepts because lots of it is old. See Xorg as a prime example. That was outdated 20 years ago already.
Closes source software gets exploited and hacked all the time. They take security seriously as well.
Look at OpenSSL and the heartbleed and similar high profile security failures for how even using high profile open source software is not automatically more secure.
You theoretically can see the code. You don’t actually look at it. Nor can you even have the knowledge to understand and see security implications for all the software you use.
In practice it makes little difference for security if you use open or closed source software.
Java has been running serious server software since the mid 1990s. Think WebObjects running on Solaris. Lots of business stuff with big databases still run infrastructure like that.
Java still has the big advantage of being machine agnostic. No need to recompile for ARM or Intel.
Early Swift was very slow to compile and start. The debugger was nonfunctional.
Otherwise it was pretty usable. Especially since it got to leverage the huge libraries written for Objective-C.
Which meant it lacked some basic collection types. A Swift native Set was introduced with Swift 3 IIRC. Before that you had to bridge back and forth between Swift and Objective-C. Sometimes leading to unexpected behavior at runtime.
In Objective-C if an object reference was nil, you could send it messages (call methods) without a problem. Swift however did away with this. Optionals had to be explicitly unwrapped. So if the annotations weren’t correct, Swift code would crash at runtime where Objective-C would have been fine. Lots of bugs related to that existed.
Swift peaked around version 4. Since then, they have been adding kitchen sink features and lots of complexity to feel smart.
I still would have preferred an Objective-C 3.0. Chris Lattner was a C++ guy and never really understood Objective-C culture and strengths.
C++ is a great language it you refrain from using 70% of its features.