This mechanism ("batch auctions") are not immune to rewarding low-latency connections. The details depend on the exact auction mechanism but the general idea is that you want to join the batch as late as possible (at any moment in time when you make a decision to join the batch, you are never worse off if you wait a while before joining) and low-latency connections can afford to join later.

In fact with your exact proposal, assuming everyone has a connection with at most (say) 50ms latency, no one will join the batch in the first 50ms, which (I think) magnifies the low-latency advantage.