Whether or not you can "feel" the out of balance condition at lower speeds, if it is there, your tire knows it, and the wear pattern will reflect it eventually. Out of balance also contributes to most of those "other" problems, except for an actually damaged tire which should be replaced anyway.
Beads have to be spinning sufficiently for the mass of the bead to be affected so as to redistribute the beads, and to be held against the inner perimeter of the tire, rather than having them cascade around inside like clothes in a front loading wash machine. Until the tire is spinning fast enough for centripetal acceleration to hold the beads against the tire, they don't do a thing. If your tire is more than 8 ounces out of balance, naturally 8 ounces of bead won't correct the problem, nor can the beads align themselves in such a way that 8 ounces will actually cure an 8 ounce out of balance condition. You need a bit more beads than the imbalance calls for because they will be strung out in the area that needs them rather than concentrated on the spot where the actual weight will do the most good.
It isn't that beads don't work. They do. Physics tells us that they have to. But how well they work as a tire balancing device is a different question. If beads can balance a tire, so can balancing weights properly applied. I figure that if I can balance a 37 inch Bogger with a Harbor Freight bubble balancer and stick on weights, any tire can be balanced with a real balancing machine and a qualified tech.