Sure, Padme would be better right now by turning her into Jabba. But they potentially fill a different niche - although I'd agree that Padme isn't really in a position to do it right now.
I was talking to a friend about mill, and he made the point that decks that plan to win by mill will generally want to discard 3 cards a turn from the opponents hand - assuming the opponent will want to play/discard at least two cards a turn themselves. The deck then basically has to survive until they time out the opponent, but there's no real way to push the clock further by discard. Milling the deck opens this up an option, but you're right - you've got to be discarding their hand first, and then mill starts to be become relevant once it starts to speed up the win condition. My impression is right now, Heroes probably can't do that reliably enough in most cases to be worth it. However, if things change, Padme may be worth it in a way she wouldn't be if she was straight discard. Of course, it's equally as likely we never see that, or she still ends up being too expensive (points/resource wise) for what she brings.
Your friend is wise.
Discard is undoubtedly tactically stronger, but that doesn't make milling from the deck bad if milling is your win condition (if not, then yeah Padme is mostly useless beyond that two focus side).
Padme's ability provides redundancy. In combination with discard effects or die sides (see the above comment about Thermal Detonator), she advances your strategy. Similar can be said for Patience. Between Padme and Patience, you could reasonably hope to accelerate your mill strategy by two rounds or more.
Padme and Patience also do one thing that discard effects cannot - ensure a mill win in spite of things like Starship Graveyard or Closing the Net that can recycle cards back into a deck.
Is the hero mill deck viable at this time? Probably not, but that could change with future releases.