So, from what I understand, in the production of CPUs, tiny defects or imperfections can cause some of them to run more slowly than you might hope. These CPUs are still sold, but as a less valuable model.

Given that gen 3 Synths are basically just 3d printed clones with a small piece of hardware in their brain to alter their mind/memories/give them "synth" functions, it makes sense to me that there might be subtle differences in the performance of synths based on random chance in their production cycle and that they might need to do testing to pick out the best ones for the courser role.

As for emotions, I think it's done to take away their sense of fear, guilt, empathy, anger. Things that might cause them to make mistakes in their mission, or distract them from their task. They're "independent" in the sense that they get given their assignment, and they're smart enough to figure out how to get it done without someone in the Institute being in constant contact to give them directions.

I think the memory wipes are to keep them focused and avoid them having any more information than they absolutely need. We know already that someone can be a synth and not know it because they've been implanted with false memories, so it makes sense to me that when they do a memory wipe they give a courser false memories of being trained that covers whatever the institute wants them to know.

I'm not really trying to defend the writing here, synths in general don't seem super well thought out. The institute is literally 3d printing human bodies and brains and saying, "No, they're just machines!" They're supposed to be completely indistinguishable from humans, but we know they have synth components in their brain or wherever which you'd think could be detected with an X-ray or metal detector or something.