The other day I had two runs where people were undergeared with initial equipment at the manor, one offending tank had level 1 armor in two slots and no jobstone which resulted in him having less defense and HP than me. I can understand having things 5-10 levels behind in the non-capped dungeons but if you end up with less HP and defense than the healer then you are clearly just trying to start a fight. A minimum item level wont work for earlygame dungeons for the reasons described above, but after a point it should at least mandate minimum defense or attack power depending on your role. Equipment is not hard to get in this game, even on F2P you are basically handed good equipment via your job quests and poetic vendors.
On that note, the argument that you could equip a Lv1 weapon doesn't hold water, because that would be considered griefing which is reportable and a valid reason to vote kick. Though it's not a listed reason on the prompt, not being able to reasonably fulfill your role is named as an example of unlisted but valid reasons in this post.