What is meant by middle of the spectrum  (MOS) groups?  I just coined the term for the purpose of this thread, so give me a minute to articulate what I mean (I'm still figuring it out) 

This thread is to debunk, to a certain extent, the idea that some artists (not all) are  judged as under-rated, or under-valued, when the truth is, they are in a valid spot, looking and sounding good, right there in the middle of the spectrum.  
MOS groups are those that fall in the middle between the far side of "obscure" on one end, and "the most famous and popular of all" groups, on the other side.  I'm not referring to middle of the road (MOR) or AOR music, or any particular rock genre.   

MOS bands might be nationally known, or have a huge regional following.  They've recorded, sold, and made decent money, and are making it as musicians.

They are where they want to be, they've been on the music scene a while, and will probably never be "the most famous and popuar of all", but that doesn't mean they are under-rated or even under-appreciated.   There are times when people call a MOS group "under-rated" but that's perception only -- every group or solo artist simply does not become mass-market famous or unendingly popular; every group does not have cross-over appeal, which, in part, is what qualifies a group to sell millions of records.

On a meter, obscure would be a "1" and most famous and popular of all would be a "10".   

MOS groups are smack in the middle, around the 4-7 range.    MOS groups have plenty of fans, but they tend to be a more targeted, subset.  They may be hard-driving tour acts that show up at lots of festivals, but are never the headliners, yet make it near the top of the heap.  Might even have household name recognition -- yet, only a limited number of households are buying their albums.   

MOS is their niche; it's a snug, suitable space for them.  

Who are some of your favorite (or best) MOS groups?   Do you agree this is a legitimate classification for a band?  They're MOS; fine, and proud of it.  

Thoughts, anyone?