I would guess that using ADB was far more of an effort than actually installing GrapheneOS.
I installed it using Linux and Chromium browser, first time of asking, in 20-40 minutes, a few years ago. It was the first device I actually flashed an OS into, not the first successful after several attempts, but the very first device and at the first attempt. I would encourage anyone if in doubt, just do it.
I like you would like a non Pixel GrapheneOS device, however I would not go near a GrapheneOS pre-installed phone from Amazon.