I agree that the "average" guest may see a marginal improvement in the SB line. But as I've said for a long time, spreading the benefit thinly among thousands has less impact than the old "unfair" system of fewer people reaping a larger benefit.
If the SB wait decreases for all guests from 65 minutes to 60 minutes because of fewer FP holders "cutting" in front of them, the difference is barely noticable for that "average" guest. They are still waiting an hour for a ride and that will still be perceived as a long wait. But in order to reduce
everyone's wait by 5 minutes, Disney had to take away the perk of waiting only 5-10 minutes for that ride from a lot of people who can no longer get a FP for it.
IMHO, this results in disappointing a lot of people without providing a significant improvement for the beneficiaries of the change. If I truly believed that the vast majority of guests would be coming away from their vacations having experienced a huge improvement, then I would not be as skeptical about the "sacrifice" others made to facilitate it. But it seems like those who maximized FP usage experience the negative impact of having fewer FPs, while there's no significant payoff of other guests having a markedly improved experience to offset that. At the risk of sounding too political, that's how re-distribution always works. You have to take a lot from those who have it in order to spread the wealth to the masses. But because the masses are massive, the resulting token pittance that each receives doesn't make a hill of beans difference in their lives.
Basically, Disney is rationing the "pixie dust" (i.e., SOME people experiencing a much shorter wait) in favor of "fairness" and "sameness" where everyone gets a SLIGHTLY shorter wait... it's still an hour-long line but, hey, we saved you 5 minutes!