Boeing hasn’t admitted anything, actually. The fact that the MCAS system can be improved does not make it the cause of the crash.
For one thing, maintenance was done on the AoA system on the Lion Air flight just prior to the crash, and other pilots successfully handled the AoA problems on previous flights.
For another thing, we have pilot reports of 737Max nose down problems when the MCAS system was inactive. These happened when the auto-pilot was engaged, and went away when the auto-pilot was disengaged. They pretty much could not have been caused by the MCAS system.
So, fixing MCAS may not stop the crashes at all.
I read a report somewhere that said that the Data Recorder showed that the Air speed reading dropped to Zero before the plane crashed. Now that would be quite a coincidence.