For those unfamiliar, Slayer is (imo the best) one of the top $$$ machines and pairing it with a budget grinder is a classic sign the owner doesn't know a thing about coffee. Often the grinder is more influential than the espresso machine.
And how I mention "Group 3" that means it has three brewing heads. They were using a ~$20-30k espresso machine paired with a run of the mill budget grinder.
The exception to that rule is Espresso Vivace in Seattle, with (at Capitol Hill location) a couple 3-group La Marzoccos at the bar and a collection of modded Niche Zeros on grinding duty. Nobody can accuse David Schomer[0] of "not knowing a thing about coffee".
It's kinda wild to look and see even the old models listing for double the price they used to.
The point is that investing in such a crazy expensive machine but not a much better grinder is really foolish, because the machine is going to be limited by the grinder so they may as well buy a machine that is 1/3 the price.
But really it sounds like 80% of the problem in the case tow OP is talking about still would have been the poor skills of the baristas, because they should still be able to pull very decent shots even with the mid-range grinder.
The same La Marzocco that puts fake paddles on their cheaper machines when whats there is really just a button?