Yes, the entire synthetic population of the planet was built by Maddox and Soong. They initially only created one pair of synths to look like Data's painting - Jana and Sutra. Maddox later decided to create another set of synths, this time not intended simply to add to the population, but programmed with a very specific purpose for deployment as undercover agents to investigate the cause of the Mars atrocity. To expedite the process, he re-used an existing design, which is why a second pair were created with the same face. Plus, since he went to the trouble of programming Dahj, the Earth-based synth, to seek out Picard in a pinch, he probably chose that particular face again because he knew it would be familiar to Picard.
Honestly, the story holds together a lot better than you seem to think, and the pieces do tie together, if you accept them at face value and make the connections, instead of looking to holes to poke at.
See, I don’t remember much of that being explicit at all. I got the impression, from the early episodes in particular, that Soji and Dahj were literally grown from a piece of Data. (Which would have been nice, and better than a resurrected Data or the Cat in a Box Data we got.)
I don’t look for holes, I just look at the way it hangs together, and sometimes it’s difficult not to notice changes in direction vs things that may be set-ups for later. The interview with Akiva acknowledges that to an extent, and there is something that feels clumsy in the ending (maybe they did plan on pick up shots with a few more of Data’s ‘family’ from the TNG days there. Otherwise you have a mentally compromised Picard making Power of Attorney decisions for a possibly similarly compromised Data.) as a result.
I mean, at one point, I expected some kind of Data remnant (like the one in the box) to be giving Picard his little dreams via the same Borg connection we know from First Contact. Until quite late in the day I expected the artifact to be relaying these little clues. Beyond a vehicle for getting Seven in the story, upping the reference quotient, and upping the horror quotient, I am not actually sure what purpose The Artifact served in the season one story, or if it is intended as part of a longer game, and whether that was it’s original intent. (Picards new body will have no remnant of his assimilation)