No, it's not a myth. Phytic acid is an antinutrient in that it removes certain nutrients from your body. Phytic acid removes minerals such as iron, and calcium. Also, if you soak beans and rice etc. it doesn't remove all of it, just a percentage of it.
This is no doubt a very difficult subject. I have studied it every which way and have decided, for the time being, to eat a small amount of whole grain without soaking. For breakfast I have less than 1/4 cup (dry measure) of steel-cut oats. For lunch I might have one slice of flourless bread (made with sprouts). And for dinner I might have less than 1/4 cup (dry measure) of whole grain pasta. If I could, I would eliminate grains altogether but I can't because I would keep losing weight and become underweight.
For 4 years I lived on a corabination of legumes and rice, pasta etc.. It was a meatless diet. But then I learned about phytates and decided to change back to eating small amounts of lean meat and small amounts of whole grain.
My emphasis now is on eating fruit, and lots of vegetables (a corabination of cooked and raw vegetables). I eat a reasonable amount of heart healthy fats which includes walnuts, olive oil, and avocados.
Occasionally, I will have some lentils or split peas.
Having said all of the above, I eat lots of leafy greens and other vegetables in the hopes that I am getting more nutrients than I am losing, by way of phytates.
P.S. Peanuts are legumes so I avoid them as much as possible.
Also, I did read a book once that was all about phytates and I posted a summary on the health and nutrition board. If I knew how to retreive it for you I would because it was more complete information than what I have provided here.