The Disk IO Manager has customized support for S3 and remote HDFS that allows for these to use a separate queue and have a customized number of IO threads. Currently, ADLS does not have this support.
Based on the code in DiskIoMgr::Init and DiskIoMgr::AssignQueue, IOs for ADLS would currently be put in local disk queues. Since local disks are considered rotational unless we can confirm otherwise by looking at the /sys filesystem, this means that THREADS_PER_ROTATIONAL_DISK=1 will apply as the thread count.
This reduced thread count may hurt ADLS performance.