Multiple decks, like 6, is what I mean by "most blackjack." Yes, the 6-deck shoe is shuffled after about 75% of those decks are played. There are certain casinos that have "continuous shuffling machines" that shuffle every hand. Those are impossible to count, but rare.

6 decks, as opposed to 1 or 2, does make counting less accurate. But ultimately everything I said previously applies. Those stats are based on the current common game of 3-2 Blackjack, H17, 6-deck shoe, no continuous shuffle, and double after split.

Counting works fine with 6 decks. And they don't shuffle after each hand - that would slow down the game so that not as many hands will get played.

Counting works but the way to profit from it is easily detected. You have to bet big when the count is favorable, and a casino will see that and stop you.

The MIT Blackjack Team beat this, with the strategy to have one player at the table who would bet small while counting cards, incurring the expected slight losses to the house edge, and signal a teammate to jump in and bet big (like $5k per hand) when the count was favorable. Casinos now know to stop this - if you walk up to a table and want to bet big, they will require you to wait for the next reshuffle (or just reshuffle immediately.)