The B737stab trim system has two speed modes for the autopilot and main electric trim, I.e. high rate trimming with flap extended and low rate trimming with flap up.
I am wondering if the MCAS was programmed to always input high rate trimming? Hence if you are flying a MAX with flap up and the MCAS puts in a high rate AND burst for 10sec, then the pilots available ANU counter response on the main electric trim will only be at the low rate.