MIMO-OFDM for PDSCH in 5G NR with QPSK simulation

Hi Experts,
I have tried to simulate MIMO-OFDM for PDSCH in 5G NR with QPSK.
When I compute the Throughput, Without HARQ is giving better than with HARQ while using ZF, but MMSE is inverse way which is more logic to me.
Is ZF cause like this when I use without HARQ that gives better than with HARQ?