Is it unrealistic to expect that vast majority of “songwriters” to be musically proficient in some way?

I see so many people here who aspire to write songs but seem to have no musical skills. I know, for example, there are some oddballs like Jelly Biafra who can not play a note, nor even sing that well, yet has a strong enough musical vision that he was able to write songs in his mind and whistle the parts to band members until they had (good) songs that worked. But this is extraordinarily RARE! Doesn’t seem odd how many people here are trying to skip the step of understanding music in even a rudimentary way and jump to writing “hits”? Seems like in other disciplines the common advice would be to learn to walk before you start to run. But, i don’t see a lot of that here. Mostly “you can do it” and “don’t give up on your dreams” type advice. Instead of what seems more useful, “Do some hard work and you may get results”. Learning how to be at least be semi competent on one instrument doesn’t seem like an unrealistic expectation when wants to compose music, right?