The alternate interpretation is that one has to "write" a holo-character, and nobody with any skill has gotten around to performing this task for the initially blank holofiles of the E-D as of "11001001" yet (and Starfleet frowns on people bringing their own characters from outside vendors on isolinear USB sticks). With time, such characters will accumulate, and be used as templates for further characters by the computer...
Riker's musings about how Minuet is "different" could be dismissed as simple flirting, and he could be a veteran of interaction with holocharacters for all we know, even if his previous starship's holodecks lacked in some other aspects of sophistication. Picard is a more objective source of amazement - but when he thinks Minuet's ability to adapt is remarkable and new, this may simply reflect Picard's disinterest in holotainment, of him being out of date for being such an old fart.
Remarkably, Picard brings up "adapting", but not, say, the fact that Minuet is aware of what she is. Then again, any interactive program might be taught this fact, exactly because the average user might be interested in this aspect, without this translating to actual awareness by our strict and ever-changing standards.
The next adjective is "intuitive", and Riker thinks this "uncanny", affirming this is the first holo-floozy he could consider developing feelings for. Has Riker never had the opportunity to purchase anything from Felix? Or is he just not the type, and is now trying this thing for the first time in his life, even though it really isn't where no man has gone before?
We might still choose to believe that holo-personalities were unknown to the Federation and not just to Picard and Riker at this time, but that the tech became commonplace within the next five years or so. If this is a pure tech advancement, then the tech itself might be new, Flotters and 23rd century Recreation Decks be damned. But it could be a change in legislation, too.
(As for Minuet becoming an empty shell, she rather seems to disappear outright. Which would be consistent with a program being yanked out, rather than a capacity being removed, I guess, since Riker "searched for her", as if from the ranks of holocharacters, rather than for a missing set of skills to install to a character.)
Timo Saloniemi