I'll confirm this. I haven't beaten the game yet, but I have all of the blackjack upgrades purchased up to and including the last extra deck removal and the spy (I forget which one came first). But I'm down to one deck, spying on the dealer, counting cards, and have one or two (I forget) winnings upgrades...
Win rate is sitting at 43%. Tracking 100 games manually I see a win rate of around 46%, so 43% overall win rate seems feasible. Blackjack returns - almost stable, but that "almost" is definitely a loss. I very briefly made money off it at some point, and it quickly went back down into the negatives and just keeps on going