We're discussing whether redistributing the board stipends would change individual salaries and the clear answer is it will not, even in the most extreme situations.
But, to your point regarding prorated comp: I've been a salaried employee at a company like Google. I've also been a board member.
First, like many senior tech employees my total comp market rate is in the seven figures. A pro-rated 1.2M stipend would be appropriate to compensate me for my time. The average board retainer for less profitable companies is closer to $30k/yr. These are not entry level positions and the retainers are shockingly low in the vast majority of cases. (In my case, I'm on the board of a non-profit and I actually pay them)
Second, I think you are underestimating how little some salaried workers actually work. I think if you try you can find more than a few Google employees who only work one month a year ;) Conversely: I work far harder in my role as a board member than I used to in my salaried role. It's different for everyone of course, but I assure you no one is seeking out board seat retainers as a way to get rich. It's just not worth it.
