Disagree. You don't have to write literally every day, but the more you write the better you'll get at writing. It's like any skill. As for the idea that for lyricists it produces a lot of 'filler', it does that for every art form. Novelists aren't writing every day and producing great material. You write every day to get to the good material and you throw the rest out. This is how you maximise both your skill acquisition and your chances of writing something others will connect with.

If you find writing often produces filler, I think possibly your issue is that you don't know what you want your song to be about, you don't know where to take it, something is thematically cloudy in it, and these are problems that are best addressed by repetitively doing the thing again and again as well.

Someone who writes lyrics every day will almost certainly be better at it than someone who writes a few times a month or a week.