It is the TouchWiz launcher that causes performance issues. Even now, with Android 5.0, it stutters when swiping from screen to screen. I had to widgets up and running two: a large Google Play Music widget and a smaller Google Calendar widget. It stutters when going from different home screens, pauses before it pulls up all of my apps, etc. I switched to the Google Now launcher and it is much, much faster. No stutters when switching between home screens (and I have even more active widgets), it instantly pulls up all of my apps, etc. PsychDoc is a little off with their assessment of what a launcher does. Launchers run independently of one another so Nova just isn't a skin applied over the TouchWiz launcher, it is a launcher all in its own. That's why the performance of Samsung devices often drastically improves whenever a new launcher is installed. Things would be much worse if launchers were just skins on top of the TouchWiz launcher.
As for disabling Google's "bloatware," I can disable some content but not others. I have to use either Messages or Hangouts for texting (those are the only two that push texts to my Moto 360 while allowing me to directly reply in them), Samsung's e-mail app is a bigger resource hog than Gmail so I'm not getting rid of that (and it looks like a mobile version of Lotus Notes from 1999), and everything else Google related isn't taxing my battery.
I've said it before and I'll say it again: Samsung makes great hardware. Their flagship devices feature the latest tech (for their time), are solidly built, and can offer great performance. The S5 was truly a beast when it came out and can still keep up with more modern phones (in some areas) like the iPhone 6 Plus. It really is a testament that a phone released almost a year ago can keep up with one released a couple of months back. But their software is atrocious, to say the least. It's the same with my Samsung plasma. It produces stellar picture quality rivaled only by high end sets that cost $3000+ (it only cost me $750), the 3D picture quality is great, gaming on it has been a treat, but the software that the TV runs is buggy, slow, and has recently caused issues like making my TV randomly restart itself or randomly showing a popup saying that Smart Hub was upgraded. Spectacular hardware that holds up almost 3 years after I purchased it but the software is terrible.