I'd disagree, though as you say, we'll need to try the cards in context before we can truly judge.
Some reasons though, that I think Aun'shi will be the Warlord of choice here:
1) Armourbane is huge. Even Piranha Hunters become a good card when they can easily gain Armourbane.A Viorla Marksman with an Ion Rifle with armourbane is answerable with Archon's Terror or Indomitable, and thats it . Even the Warlord carries armourbane, making him straight off the best solo combatant there is, with his 2/7 stats. Forced retreat might be problematic, but mostly this weakness is a boon: you don't have to waste your first action fleeing from Ragnar and his Honoured Librarian: you can attack AND flee.
2) The signature squad is a 1 cost superb command capper that can survive a small snipe attack and still retreat after counterattacking. That makes for a nice easy cost curve, straight off.
3) Ethereal Wisdom is a true 0-cost event. A lot of 0 cost events have costs in the text, but not this one. The +1 attack synergises with armourbane, making the deck very hard to answer.
4) Homing Beacon. It barely works at all with Shadowsun decks, but is superb card draw for an Aun'shi deck.
5) Most of the things that make Shadowsun decks great lie outside of the sig squad. We can still use Ion Rifled Marksmen, we can still use Recon Drones, we can still run Trailblazers.
An Aun'shi deck, to me, is likely to be one that uses a lot of cheap Tau units, draws like crazy through non-command effects, still does well in command phase, and is solid and hard to answer in the combat phase. That to me comes together to say tourney-winning warlord.
Offcourse he has it's advantages but the way Iniative works with Warlords on planets I am not a fan at all. In special because I feel Tau are far better equiped for the lategame because of the way the Core Warlord works.
To sum up my reasons I could use the same sum up:
1. Armorbane indeed is great, however being forced to retreat after a single combat round means your not well set up for battles against Space Marines, Chaos Space Marines and Eldar, basicly any unit that is X/3 becomes a problem if you do not have Ion Rifles. Besides that there is also no "free card advantage" that is generated by this Warlord. I feel Armorbane alone on him would have made him excellent but Armorbane also feels mostly relevant in the lategame where combats consist out of multiple combat rounds where Aun'Shi will not be around. Apart from that the current Tau units also seem to be designed for being equiped with Attachments in order to actually win battles. Again I do not see how Aun'Shi's battles will favour you in winning battles against 3 of the mayor proven fations. I do hope Tau will get more and more "fatties" but currently I cannot see them winning many battles with a multitude of 1/X dudes that also have a Warlord that is forced to retreat.
2. Signature squad that does indeed have a nice single Command Icon but also leave the battlefield early on, leading to battles they will continue to lose. Again, more than the Warlord, I am not a fan of the concept of 1 drops leaving the game early on. This can mean that when they get hunted by an opposing Warlord they will always lose the battle because they leave. Imho they are good but not what this Warlord really needed. Now if they where 3/1's or 2/1's for 1 I could see much more reason and application behind them. It's nice that they stick around but a multitude of 1/X's dude is not what Tau is lacking in it's core set.
3. Ethereal Wisdom is a nice card for sure, it will often mean that Aun'Shi will at least win some battles against Space Marine units or the X/3 units. Ditching a card in order to do that imho is less usefull. Again it's cheap but ideally you want to have a multitude (3) of cheap cards and heavier costed cards to a lesser extent (2).
4. Homing Beacon is a fantastic card for sure, I feel that if the Aun'Shi deck will work this card is a must include however, there are only so many ways to find it and imho without it I feel the Aun'Shi deck is siriously lacking hitting power and stay power.
5. Is the point where I really dissagree with you, imho what makes Shadowsun such a great Warlord has to do with the number of great attachments available (Repulsor Impact Field and Ion Rifle) and the fact that he can also attach his own Stealth Cadre with his ability. Leading to 5 cards from his own 8 being able to trigger on his ability and having 6 others available within his constructed deck able to attach out of hand and discardpile for free. That is slightly more than 1/5th of the deck and with Earth Cast Technician your able to find even more pieces.... All in all I feel the synergy is to great to switch over to an Warlord who "only" grants you Armorbane.
6. Aun'ui Prelate on the other hand imho is a fantastic addition to the Tau army. With 4/3 stats for 4 your willing to retreat after you've dealth your last 4 damage with him, it also helps a whole lot when you want to deal that extra damage in order to make sure your opponent cannot shield his way out of it, which imho is better as Armorbane because Armorbane actually is only relevant if your opponent has enough Shield Cards to work with in the first place.
An Aun'shi deck to be is one who is likely to use cheap Tau units and draw like crazy from non-command effects. However due to the way the deck works in combat will not do incredible well in the command phase and is easy to awnser in the combat phase unless the Tau player finds a Honor Blade, who completly boosts the way the deck needs to be boosted, however due to the way it can draw like crazy is able to find the Honor Blade hopefully fast enough in order to win combats afterwards. In my eyes that's a high risk high reward deck some really like to play but lacks the consistancy for Tournament play.