I would see another vet. I have never heard of anyone recommend keeping it unwrapped. You want to keep it clean and dry, but wrapped. I would also see one if you can because these infections can go systemic and kill the duck. My first Pekin got a really bad infection from stepping on metal that I didn't know was on the property. I took her to the wrong vet and lost her because of it.
When I have treated bumblefoot at home on my own, I soak once a day, and I will occasionally skip a day for my own sanity. I soak in iodine and epsom salt for 15 minutes. If the scab is not soft to pull off, I wait another day or two. I puts gobs of triple antibiotic ointment without pain on the wound, place a gauze under it and wrap the foot with vet tape. I do that just once a day. With my Pekin, I always treat with baytril. Once you get the scab off, if you can clean it out, fill the wound with triple antibiotic ointment.
Have you had any better luck wrapping it? If not, I can take a picture of how I wrap my duck's foot. I am treating my Pekin as well, so it would be no trouble to take some photos. They tend to get bumblefoot easily. Sadly, you will probably see this again. You can also try duck shoes.
https://crazy-k-farm.myshopify.com/products/birdy-bootie-hand-made-in-the-usa
That all being said, vet is best at this point. Those veins showing worry me that they could be a sign of the infection spreading. I really hope the best for your duck.