I have seen AUJ a gazillion times and kept looking for Bolg, but never quite figured it out (possibly because I kept looking at Thorin but NOT my fault). This helps me immensely.
This is a good theory. The idea of orcs as corrupted to begin with, further corrupted by Sauron, definitely explains the appearance difference. I do think the goblins of LOTR were scarier than these ones (I'm assuming those were goblins in Moria, but only because Legolas said so).
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I think Bolg is deformed because of what Dwalin did to him at Azanulbizar. He doesn't look half as bad in the pictures of him before that (he still looks pretty terrible of course).
Other than that think your theory is pretty accurate. I wonder if the orcs prefer life with or without Sauron around?