@pulseman45 you're right. a lot of features from other manufacturers' skins have later been integrated into pure Android. And yeah it's a bit of a pain that even the Pixel phones or the Android One phones receive system updates for only two years and security updates for 3. I suppose the argument of the manufacturers is that after that time, a new software update would slow down your phone and therefore hinder your user experience. And once again, you're right about ROMs being a way to deal with this, and get the latest and greatest of Android on your phone, but I see you're also aware of the risks of installing a ROM.
@Omar Alvarado unfortunately, phones tend to become slow over time. That could be one reason for the slow down of your keyboard. You can either try different keyboard apps from the Play Store (I like Google's own keyboard, Gboard, or Swiftkey), or for something more radical you can do a factory reset on your phone. If you do the factory reset, however, all your data (pictures, files, saved passwords etc) will be lost, so you'll need to back them up first.