The pilots on lion 610 were in regular contact with ATC and as late as 20 seconds before impact with the ocean they indicated their preferred flight level. This suggests they were not under duress in operating the aircraft until the very end. It is still very much unclear why their successful and consistent NU trim corrections are suddenly insufficient to counteract MCAS.
My understanding is there was a change in which pilot was flying near the end of the flight. The original pilot dealt with the ND trims with NU trims consistently. This can be seen pretty clear in the FDR traces. Each ~10 second ND trim is followed by ~10 seconds of NU trim. Then after the change of flying pilot, the NU trims are only a second or less at a time, and never really counter the ND trim at all.
The question is why the change in flying pilot? The CVR will go a long way in answering this, if it can be found.