The idea behind this one is that, rather than choosing your commander first, you decide on what your deck wants to do first
There are other cards with simliar effects, so you can build a deck and rely on getting one of them, even if prophet is the best, there's also Wilderness Reclamation, which is nowhere near as strong, but still good (also banned itself in standard) and Murkfend Liege (only creatures though, and only blue and green ones) Unwinding Clock, only artifacts, and Seedborne Muse, which does more untapping but doesn't give Flash
Scammer selling fakes are artificially aging the cards
If Drowner of Truth is countered or otherwise leaves the stack in response to that triggered ability, the triggered ability will still resolve as normal