I have friends Ive dated then figured out we're better as friends, I have had relationships out of friends, Ive got friends I wouldnt date (both because we just arent attracted to eachoyher but also because although we're compatible we're better off platonic), I dunno if I would tell people to just go up to their friends and ask them out though over and above asking a stranger or acquaintance out intentionally lol. I think if the advice is, like, you're probably better off getting to know people before jumping in to asking someone out, thats all well and good - but I definitely wouldn't rate asking out friends higher than a stranger.
The Friend Zone, conceptually is one party has a huge crush on the other and is intentionally or unintentionally strung along - unintentionally being strung along isn't really a thing but you get it. It does seem like way more a thing cishet dating than anything queer fwiw. Its definitely better to like ask someone out if you both know each other at least a little but Ive also been out on dates and had a relationship with people Ive asked out off the rip and people whove asked me out as a stranger. I definitely wouldnt say it is necessary to be friends first. Actually, Id find it a bit rude if I had someone I considered a dear friend reveal they only wanted to be friends to pass some imagined necessary middle stage of being a friend before asking me out.
Also, who's to say a dynamic is easier or less confusing just because you were friends first? I don't think that's accurate to be honest, it's a big change and new if someone makes the leap between friends to dating - who knows, it could be just as mysterious as meeting a stranger you really fancy and asking them out.