I think all methods are viable and have different strengths and weaknesses. Probably in a general sense, the thing you start with will probably be the better of the two and it will take more work to get the other one to match. You can have a great poem, but putting it in time might be a struggle, or you could write a great melody but finding words with the right syllables to match could be hard.
So probably try everything, and do what's most appropriate for the song at hand.
I like being abstract but that's just me. Sometimes I'll just write out ideas in long form and take phrases out that roll off the tongue the best and use those as lyrics. I don't like being very literal either and tend to go for metaphorical phrases that get people thinking of their own interpretations rather than just laying out what the song is about. When I'm tracking vocals, and it's been well over a year since that has happened, I'll often have to edit things as I go. Just part-and-parcel of singing.
As for the jist of the question, ftmp I write lyrics after all the instruments are done.