I believe the Stihl MS 170 is no longer made. The MS 172 replaced it. At 10.4 lbs for the powerhead only, it should meet your goal of under 12# even when the bar is added. However, a 32cc, 1.9 HP saw would definitely not be my first choice for cutting 10-14” logs, especially not if they are hardwoods.
In the Stihl line, for a homeowner/landowner saw, I’d look at the Stihl MS 250. At 10.1# and 3.0 HP It’s lighter weight and 50+% more HP than the MS172. It’s a nice combination of light weight and reasonable power for the size wood you are cutting. If your present saw is significantly bigger, it may take a bit of patience and getting used to when cutting hardwoods, but lighter weight does generally have that downside.
A similar Stihl saw is the MS251 “wood boss”. Same power as the 250, but weighs 11# for the powerhead only. For that extra weight, you get their aitomatuc carb (self-adjusts the mixture for various fuel and atmospheric conditions, so no need to manually adjust the mixture). (I’m not really a fan of the MS 251 C-BE. It adds their easy-start system and more weight. I’ve heard multiple complaints about the tool-less chain tension adjustment.)
I’d put a 16” bar on either the MS250 or 251. Many dealers will sell it with an 18” bar. but I find a 16” bar better match for the powerhead only and balance of the saw.
In the Husqvarna line, look at the 450. At 3.2 HP and 11.3#, it’s a little heavier and a little more power than the Stihl 251. I’ve used one in the past and a friend uses it as his primary saw. We’ve found it a reliable saw.
The above are considered mid-range “landowner” saws. They’ll hold up well, if you treat them right. I tend to lean toward the pro-level saws myself. (I don’t cut wood professionally, but tend to be a lot more involved than the typical landowner in my forest management.) they cost a lot more, but tend to have a significantly better power to weight ratio they are also designed to run all day, every day. They are overkill for many users, but if you are interested in hearing about them, I can make some recommendations.
Echo also makes some good saws, but I am less familiar with that line.
Two final thoughts:
1) You may hear from a lot of fan-boys who claim their favorite brand is the only way to go. That is mostly BS. The three brands mentioned above I’ll make some good sauce. They also have a couple of nuts so great, “disposable” saws in their lineup. Unless you happen to be a chainsaw mechanic, more important is to buy from a good, reputable dealer who services what they sell.
2) You probably already know this, but the best performance enhancement you can make on any saw is to keep a good, sharp chain on it. Learning to sharpen is not difficult, with some of the guide tools available. If that’s just not in the cards for you, carry a spare chain or two. Either sharpen or swap at the first sign your chain is losing its edge.