I'm curious what you think the latencies of 50,000 distributed transactions becoming a consistent chain add up to?
Each L2 is its own chain that uses its own sequencer/s. The blocks from this chain are then compressed into a single blob of data with a ZK proof that the transactions are valid. The validators on L1 only need to verify that ZK proof matches the hash of the submitted data, which can be done in a few ms even if the L2 did 1M+ transactions.