What is the length of the queue only-hardware-queue?
“only-hardware-queue leaves interface with only hw transmit descriptor ring buffer which acts as a queue in itself. Usually at least 100 packets can be queued for transmit in transmit descriptor ring buffer. Transmit descriptor ring buffer size and the amount of packets that can be queued in it varies for different types of ethernet MACs.”
Taken from here: https://wiki.mikrotik.com/wiki/Manual:Queue