Installed the latest upgrade, and all I managed to do was to slow the phone down significantly. I know the upgrade cycle is coming up with the upcoming launches, but doing it so blatantly is not kosher.
This is incorrect and a silly thing to say. Why would they pull an Apple and slow down the correct phone you have which will heavily disuade you from purchasing another Samsung phone? This is actually caused by natural degradation of phone batteries causing a less stable power supply to the phone and in turn the phone slows down.
Anyway, I would recommend starting off by going to 'settings', 'device care', 'battery', and 'battery usage'. This will let you see all of the apps that are using battery on your phone. See the apps that are using battery and make sure to delete/uninstall the apps that you either don't recognize or don't use. (Go to 'settings', 'apps' to delete apps)
Check the google play store for any app updates, check the 'galaxy store' for any samsung app updates, then check your phone for any OS updates.
Once those have completed, make sure to clear the cache partition on your phone. That should help you.
Please update this post after you try those things.