The real problem with the older MacBooks (Pro) is weight really, for a machine that I have to carry with me every day.
As far as I know, there aren't that many 13 inch or less light options with more RAM outside of Apple either.
In comparison the MBP 2012 and a MBP 2016 do not differ in weight so much (1.4kg vs 2kg which is basically a package of flour) and if I am honest I don't really recognize the difference when carrying them in my backpack.
But it depends on the bag as well, because if you use a messenger bag for example the strain on the shoulder and the back is probably noticeable. Also many people like to carry their notebooks around with one arm / hand and of course this will be a huge difference then.
Some people like to use the Thinkpad X1 or the Dell XPS as a replacement but I don't have any hands-on experience with those.
I hope someone will recognize the gap in the market and jump in to produce 13 inch, retina screen uni-body metal notebooks with the ability to upgrade the parts and with all the ports you still need when not living in some bubble where magically everything was converted into USB-C overnight.
Of course 16GB is the max. you can put into an MBP 2012.
But: Who needs that anyway? Yes if you do heavy tasks like 4k-stuff and 3d-rendering but for most tasks you do with computers it's quite sufficient.
Personally I move my tasks to servers if they need more resources.