cluster.routing.allocation.cluster_concurrent_rebalance only affects rebalance operations, but moving shards due to a disk watermark are different (and higher-priority) so they are not sensitive to this parameter.
It's almost always best to leave cluster.routing.allocation.node_concurrent_recoveries set to the default of 2. If you want faster recoveries and your system can handle it then increase indices.recovery.max_bytes_per_sec instead.