In general, I strongly agree with you. If Sim has done well, more power to him. However, I'd like add one additional point to you comments... It has been my experience that playing the long side only tends to make some traders "see" a good long opportunity when it doesn't exist. I.e., if you don't care whether you go long or short, you will look at your analysis results with an unbiased eye. For example...
If you are long player only, you might discount weak volume on a bounce in favor of the positive price movement. "Price is moving up. I gotta buy now." A more balanced trader would look at the data and say, "Mixed signals. Hmmm. I'll watch it a bit longer. If volume strengthens, I'll buy. If volume continues to weaken and then it look like it's peaking, I'll short. (No problemo.)
Even if a trader doesn't like to short, I believe that they should feel just as comfortable with analyzing for shorting opportunities as analyzing for long opportunities.