Yes, that is absolutely the most ridiculous thing I've ever heard of! It just flat out makes no sense at all! Different proteins do not fight for absorption - the only time protein fights for absorption is when you take in too much at one time, because your body can only assimilate so much at once. Therefore, mixing up your protein sources, with different digestion times is actually the best thing you can do, because your body will be able to assimilate the most of it! That's why mixing Whey and Cassein is a GOOD idea - you get a constant supply of amino acids over a longer period of time.