Um... just tried a free Mastering session at LANDR.
No apparent Sonic difference, and it seems that they just pushed my song through a Hard Limiter to a peak of -0.02dB
WHAT THE!!!!!!!!
 
See my screen grab of Amplitude Analysis upon inspecting it with Adobe Audition.

AdrianNewington
No apparent Sonic difference, and it seems that they just pushed my song through a Hard Limiter to a peak

Maybe they determined that was all you needed.
 
You didn't expect it to take Blowin' In The Wind and turn it into Dust In The Wind, didjya?

Just say NO, and do it yourself.

I have to admit, LANDR does a much better job than I would have expected from an automated process. Probably as good a job as your average DIY ME.
 
That said, it does take a generic approach that, as you suspect, is primarily running it through a limiter and a multi-band compressor. A good mastering engineer would be capable of far more. But LANDR's still a reasonable alternative for someone who doesn't want to invest the time to learn mastering for themselves.

-14 rms is not bad.....
 
-0.02 db is cutting it too close....
you can easily trip into clipping land when reducing that file to mp3 or aac, etc


 
the interesting thing to do would be to analyze the dynamic range....
see what they did to that.