1) MAG-10 has much more leucine added than whey has naturally. We are talking on the order of 5g or so (I don't have the specific breakdown because Biotest has a proprietary formula, but looking at the numbers on the back of the bottle it's pretty straight forward to estimate--leucine is most likely between 4g-9g depending on how much citrulline malate is in each scoop). This is much more than a scoop of whey protein contains naturally.
2) Speed depends on the degree of hydrolysis. Not all--or even most--of the "whey hydrolysates" on the market are anywhere near as fast as the casein hydrolysate in MAG-10 or PeptoPro. This is a simple cost cutting procedure on the part of the companies--extensively hydrolyzing whey down to di- and tri-peptides is both expensive in it's own right than just running it through 1 or 2 passes of industrial hydrolysis (to get large peptides), and more problematic from a flavoring standpoint because the small peptides are, to phrase it nicely, bitter as fuck-all.
Additionally, thus far data from studies indicates that only di- and tri-peptides can be absorbed without first being subject to brush border hydrolysis, which slows down nutrient transport by taking things. di and tri peptides absorb even quicker than free amino acids.
So, in order to get a true "whey hydrolysate" that acts "as fast as" casein hydrolysates of the same degree is very expensive and consequently not done by most companies. Most proteins billed as "whey hydrolysate" are not nearly as fast as they would like you to think. Faster than isolates or concentrate, yes. As fast as you think? Not nearly. So pick your "hydrolyzed whey" protein very carefully if you really want the benefits.
Therefore a mix of the two may not be superior, particularly if the whey has a low degree of hydrolysis or not enough di/tri peptides as a % of the serving.