Marvin, Wendy, and Wonderdog may be powerless, but the Wonder Twins were useless. These three used their minds more often than not.
Sure Marvin was a bit of an idiot at times, but all three at least were helpful to the Super Friends/Justice League. Wendy especially. I would have rather seen them than the Donny and Marie Osmond knockoffs known as the Wonder Twins(the idiot elves)