Not sure what context it was in, but there have been studies done that prove marinades only penetrate to a depth of 5mm. So, as a tenderizer, marinades are of no help.
For someone to say that there is no taste difference in various rubs and marinades, that is simply not true. However, if they were talking about the finished product with a generous slathering of sauce, as most people do, then they may indeed have a point. Simply because the dousing in the sauce will be the only flavor you taste.
Witness my experiments with Jumpin' Jim's contest chicken technique. The thighs are submerged in your sauce of choice for 1 hour and I found there is NO difference in the type of rubs you use......the sauce overpowers everything. Obviously not a bad thing in this instance as Jim was the overall winner in the chicken category.
That's why most BBQ aficianado's only use a little bit of sauce on their Q...NOT a generous slathering.