Certainly there are any number of kinds of people that tend to collect together, either by simple co-location, cultural ties, languages, races, backgrounds, common histories, or many other things. Countless variations and combinations. None of this relates to "class" as we are talking about it.
Again, I see no reason why anyone would divide people into sociological or income "classes" except as a political tool. Which, I've noticed, is pretty much the ONLY reason it's ever discussed at any great length in academia or political settings.
What have people got against individuals? The people I know have a marvelous variety of history and circumstance, just in their own lives alone. What they are is what they have become to date, and what they will be has yet to be determined.
If you look at the five "work" categories you defined, I've been in every last one of them, and sometimes more than once.
Maybe trying to define "middle class" is as bad an idea as trying to precisely define "colored" in old South Africa. When it comes down to it, who needs to know, and why?
The Westerner
My fathers sleep on the sunrise plains,
And each one sleeps alone.
Their trails may dim to the grass and rains,
For I choose to make my own.
I lay proud claim to their blood and name,
But I lean on no dead kin;
My name is mine, for the praise or scorn,
And the world began when I was born
And the world is mine to win.
They built high towns on their old log sills,
Where the great, slow rivers gleamed,
But with new, live rock from the savage hills
I'll build as they only dreamed.
The smoke scarce dies where the trail camp lies,
Till the rails glint down the pass;
The desert springs into fruit and wheat
And I lay the stones of a solid street
Over yesterday's untrod grass.
I waste no thought on my neighbor's birth
Or the way he makes his prayer.
I grant him a white man's room on earth
If his game is only square.
While he plays it straight I'll call him mate;
If he cheats I drop him flat.
Old class and rank are a wornout lie,
For all clean men are as good as I,
And a king is only that.
I dream no dreams of a nurse-maid state
That will spoon me out my food.
A stout heart sings in the fray with fate
And the shock and sweat are good.
From noon to noon all the earthly boon
That I ask my God to spare
Is a little daily bread in store,
With the room to fight the strong for more,
And the weak shall get their share.
The sunrise plains are a tender haze
And the sunset seas are gray,
But I stand here, where the bright skies blaze
Over me and the big today.
What good to me is a vague "maybe"
Or a mournful "might have been,"
For the sun wheels swift from morn to morn
And the world began when I was born
And the world is mine to win.
--Cowboy poet Badger Clark, b. 1863