I have both an old Kindle Paperwhite 2nd Gen I think and a Kobo Clara.
The kindle 'lives' in the car and the Kobo at home so I always have something to read.
I use Calibre to sync to both.
Rather than directly accessing Amazon from the Kindle I download bought books to my PC then strip the DRM - so I can read the same book on both the Clara and Kindle.
See: https://github.com/noDRM/DeDRM_tools
I'd say that the initial awkwardness is from deliberately not connecting the Kobo or Kindle to the internet to stop them from 'phoning home' when you set them up. The Kindle is easy - just don't connect it, the Kobo seems to insist but there's a simple step-by-step to bypass the enforced sign up on the Clara I use.
See: https://yingtongli.me/blog/2018/07/30/kobo-rego.html - basically SQL commands.
and you can get firmware updates for the Kobo devices via
https://pgaskin.net/KoboStuff/kobofirmware.html
and they are easy to apply - drag / drop.
I don't get books from Kobo's site as it used to be hard if not impossible to strip the DRM from them - which meant I couldn't read them on my Kindle.
Hope that helps.