This is just hindsight bias. If these employees had been paid the equivalent additional amount in cash would you have suggested to them to invest all of it in their employer's stock?
No: the point of hindsight bias is that you’re able to make better decisions when you know how the future will go. Hindsight bias that those companies will all grow in that five year period doesn’t change the way you would decide if you should invest in your employers stock today.