I don't think overskimming is a myth at all. A skimmer will remove organic compounds that adhere to the bubbles in the reaction chamber. These compounds are not just "bad". IMO
In small tanks especially an especially efficient skimmer will remove phytoplankton, small zooplankton, bacteria and many minor and major trace elements. This may not matter if one is only keeping fish. Corals however have been shown to feed on planktons and bacteria.
I think that skimming is a double edged sword. On one hand it removes organic waste and helps maintain proper water chemistry. Skimmers may also help maintain proper pH by removing carbon dioxide from the water as it is passed through. The down side to skimming as mentioned above is the removal of organics and inorganics that corals and inverts thrive on.
Many tanks run skimmerless with only live rock, a sand bed and good water flow as filtration. I have run my tank with the skimmer and without and currently use the skimmer as a means of carbon filtration and to blow off excess CO2
which has decreased my nightly pH swing. IMO
..the decision to use a skimmer should be based on the aquarists taste and the need to control organics, not just because everybody says "You have to have a skimmer"