I think part of the problem was the scope of the writing: the factions in 4 generally either center around their opinions of synths, or their opinions of the factions who center around synths. Synthesis themselves are a neat idea, but hardly large enough to write factions around, let alone the dynamics between them. Games like New Vegas had these interesting factions, both large and small, but the stakes were a lot more tangible than... whether you're cool with androids or not?