MTG: Wither and Infect on the same creature?

So wither says the creature deals damage to creatures in the form of -1/-1 counters, and so does infect. That is a replacement effect that is static, so the damage is never dealt; it it just replaced twice. Since it only replaced twice, the damage amount is still the same, so it is merely redundant. So it redundantly deals damage in -1/-1 counters, just like multiple instances of deathtouch redundantly kills creatures, so the nameless 3/3 flier (angel of mercy) only receives one poison counter.