Both of your assumptions are wrong.
A friend of mine was a professional gambler for about 10 years, primarily Texas holdem. He had first-hand knowledge of strategies casinos would use to entice "whales" to come in for a stay, and, the plants used to get as much money from them at the card table as they could. I've seen a few gambling movies, but that has nothing to do with what I posted.
As for blackjack, I wasn't referring to card-counters. As you wrote, counting into a modern shoe is next to impossible. These are players that simply are/were very good and consistently beat the house. As soon as the casinos see a trend, they often get black-balled. Seems disingenuous to me, but that is their legal right.