Further, it’s rare for the managers giving the 100% top performance evaluation to individuals to be leading groups with high overall accomplishment/delivery. (Occam’s Razor suggests that it’s evidence of poor leadership to be squandering the ability and contributions of all these high-performers. An analog might be an MLB Manager with All-Star players at every position and turning in a 0.500 season; they should expect to be fired.)
Sure a manager can affect performance but ultimately it's down to the individual.
And happiness is all nice and good but if work is the only thing that affects your happiness then you have some deep self-discovery urgently pending.
Under such a moronic system, with your reports' welfare on the line, I believe marking everyone as a top performer is an admirable form of rebellion.