The other reason Alpha is not more prevalent in tournaments is because she's not widely available to all players - unlocking her is a drawn out exercise, followed by bothering to learn her. So the player base for the character would be extremely low, yet we've seen her represented in a number of tournament top 8's and finals.
I'm satisfied that the above explains her presence at tournaments, and the arguments made about her overly-powerful advantages are very compelling. I usually say "wait and see" but in this case happy to support.
There will be opportunitiy to inspect the character's (over) viability with DOA5U having her unlocked at the start, easier to test.
At this point, you either ban, then request patch so she can come back to tournament play, or allow it and ask for patch, hoping for the best.
The problem with the second scenario is the potential damage to the quality of tournaments before a change. My feeling is Alpha warrants ban, then patch, while Sarah warrants "watch", then patch.
A few other characters are in the "watch" category, but more for not having good enough tools/too many restrictions (eg Bass, others have argued Eliot)