I tested moly coated bullets quite extensively several years ago for F Class. My findings were that there was a velocity decrease as well.
I find that to be a telling point to the defectiveness of moly as it is sold as a lubricant. If it is actually a lubricant, then velocity should increase, not decrease.
But there are those regurgitators out there who will repeat verbatim the advertising rhetoric as though it is fact.
I found no benefit whatsoever to moly coated bullets and discontinued their use, but I still have about 600 moly coated AMaxs that I'm looking for an excuse to get out of the gene pool in the ammo cabinet. They've been sitting there for 10 years. Just cant bring myself to bother with them.
Moly is also hydroscopic, so having it in your bore can be expected to draw in moisture and whatever fun comes with that. So oil your barrels well if you use moly.