Respectfully, please explain to me how writing A B C on your fretboard helps you learn bass.
Gladly.
See, I also play the piano. On a piano, you don't need to outline notes because you can see the shapes due to relations of white and black notes. The note "G" will always look the same in every octave, and there's only one per octave since piano is linear, and has no parallel "strings" of notes going on.
On a guitar, however, things aren't the same way. Not only can you find the same note in its octave in multiple places, there also isn't an obvious shape-based outline that'll show you exactly which note would be on a certain fret on a certain string.
Look at it this way: if you zoom in the piano so that you only see 4 white notes total, you will know with 100% certainty which note each of those is. If you zoom a guitar's frets so that you see 4 frets, you will be able to outline their relations but will have no clue which notes those are unless you know exactly which part of the fretboard you're looking at. Inlays are designed to help with this, but they are obviously inferior to having a WBWBWWBWBWBW keyboard outline.
In essence, your question is akin to saying "how does having sets of two and three black notes help you learn the piano". You may not believe in visual aids /feedback in playing, but if so, just play blindfolded, sight is a crutch, after all, how did Ray Charles play? If "blind" was good enough for him, it should be good enough for me, too.
inb4 "remove inlays they are a crutch for bad players"
There's no need to make playing harder than it already is, the notation system we use today was designed to be used for and by keyboards, which show white notes as C Ionian, and not by guitars, which do not show the actual notes clearly enough, but may show relationships between them a bit better in some instances.
Well, playing the bass is easy enough, it's mostly just hard if you want to get really good really fast since that just kind of doesn't happen unless you're madly talented and/or committed.