This statement is so patently not true. The game hasn't changed suddenly. Over the course of the past 20 years? Absolutely agree with you, but over the past 2-3 years? No. Not to any significant amount.
Most M2m's aren't airtight. All M2M's allow good players to get good shots.
The zone isn't airtight, and never has been airtight. And, oddly enough, good players have been able to get good shots off it. This has been, and always will be true.
However, a good zone, just like a good M2M will make players make uncomfortable shots. Many players will miss a higher number than average of those shots.
These guards do not make players take uncomfortable shots. Or at least, very, very few.
It's the players, not the game.