I felt just like @cxk (chris bizzelle) until I upgraded from Mavericks (10.9) to High Sierra (10.13). Yes, I waited that long, because everything Just Worked. But eventually some of my apps were no longer supported and Homebrew was not supported.
What a difference. Instead of 1-3GB free physmem under my normal app load, I’m at roughly 300MB. Mail.app takes literally 500 to 800 milliseconds to respond to keypresses requesting things like “delete a message” or “display next message". Instead of ~250 entries in the process table for an idle, no-Apps open state, I’m closer to 300.
This is clearly not a criticism of the 2012 MBP, but rather of Apple for making a wonderful machine slow by releasing a bloated, poor-quality macOS release. They ought to be ashamed. If I could find a copy of the 10.11 installer, I’d seriously consider going back to an older release. Oh I know — they want me to buy a new laptop instead! I like the features of my current MacBook Pro, thank you very much. Grr.