Hi - sorry for coming to this discussion late - I've not been on the forums for several months due to other things getting in the way but... I am a SM2 GM, exclusively using the 2nd ed rules although I've picked up a few Privateers books (not the core one yet though) so a shift may come eventually.
My take on the AT situation is simple - AT9-12 is better against high tech weapons than 13-16. Just because it has a higher AT doesn't mean it's better! 13-16 are mesh armours, which originated from the old RM chain mail armour types, while 9-12 have their roots in rigid leathers - i.e. a tough-to-penetrate material which has a bit of give to it. You will note that these days protective body armour is not made from mesh... it's made from rigid plates - against a high speed bullet, meshes would perform no better than chain mail does against crossbow bolts. So yes, it's an anomaly, but having the AT progression from 12, 19, 20 doesn't inherently break the system - it's not like there aren't a lot of armour types out there.
There's not much around for additional material these days since SM2 came and went before the internet really took off. I can of course recommend the adventure series I uploaded to the download section of this site, which was written for use in SM2. I have another adventure I need to upload there at some point in the future - scenarios 1-8 took about 20 weeks of play, but scenario 9 took 6 weeks all on its own (I was expecting 2, maybe 3) and the group has not yet finished scenario 10, and I was wanting to post them up faster than one at a time.
There are some robotics rules in the core books, and you can also find some humanoid body rules using the cybernetics rules on SpaMCo2 (although they have some discrepancies - I've also done a stream-of-consciousness thoughts on that, also in the download section).
I do love the rules and setting even though there are gaps in it large enough to drive a truck though - I hope you continue to play and enjoy, and as fellow SM2 GMs, maybe we can compare notes from time to time!