Your logic fits and, as some of the commentators have stated, I've pondered about this in the past.
Usually your dominant hand naturally can handle doing a lot more work, like you've stated. In playing instruments, the dominant hand also should be used for doing the "big jobs":
- in drumming, the dominant hand would be hitting the hi-hats. In a normal 4/4 measure, the dominant hand would hit the hi-hats 8 times, whereas the other hand would hit the snare once or twice.
- in tabla, the dominant hand would play the fine tuned dayan. Once again in a normal 4/4 measure, the dominant hand would be playing 6-8 notes, whereas the other hand would play anywhere from 2-4 notes.
This also goes for the guitar. If you're playing rhythm, the dominant hand is doing all of this work, upstrokes, downstrokes, arpeggios, string skipping, etc., whereas the other hand is simply fretting a chord.
Picking/strumming can require big/quick/exact movements. Fingering and fretting gennerally requires smaller, more dexterous movements.
I guess the misconception/myth is that picking/strumming is less work than fretting. I wouldn't say that one is more than the other, it's just different types of work, and generally, the dominant hand is better suited for picking/strumming.
Note: There are some people who are dominant right-handed and play left-handed, and vice versa. In the end, it all comes down to whatever is the most comfortable for you. Nowadays, there is no lack of left-handed guitars available, so if you find it easier and more comfortable to play that way, go for it!
Also, see this page which has some more information in deciding whether to play one way vs. another.