You're missing the point. The comparison isn't everyone taking a single car vs using Uber pool, the comparison is people using Uber (pool or not) vs using public transit.
Uber pool might lower the amount of greenhouse gases compared to everyone using individual Ubers, but that is a drop in the bucket compared to the increase from people using Uber instead of public transit
Uber pool might lower the amount of greenhouse gases compared to everyone using individual Ubers, but that is a drop in the bucket compared to the increase from people using Uber instead of public transit