Yes, but keep in mind if you go mining for iron to make enough buckets and go hunting for enough liquid, you deserve same speed of everything. However, this is a fishing reward and has infinite of all liquids,so there should be a drawback, and this is also so if you want a little bit of lava, you don't flood your house with itWell, if liquid buckets were stackable, like empty buckets, then, when pouring a stack of liquid, you would get the same speed for any liquid, so, endless buckets should work the same way, as an infinite stack of liquid bucket.