If you get a galaxy S4 now, it's not the fastest, but perfectly usable phone.
https://arstechnica.com/gadgets/2017/09/ios-11-on-the-iphone...
Same thing happened to iPhone 4 a while ago, it was literally killed by iOS 7.
I'd rather not update in this case.
Also, google is sending security patches for older versions of Android. Latest one for S5 is from beginning of 2018.