MCAS it is correcting the design defect due to put larger motors. Without MCAS that aircraft do not meets the certification requirements for to fly.

This video is about bledend-wing designs, but it touches on the 737 MAX problem with illustrations,

https://www.youtube.com/watch?v=59A8-rKRs-0&t=705s

at minute 11:45 , but it's also worth watching the part at 4:31 , where another illustration explains the forces at work in an aircraft, using a classic 737 as an example.

It is on a different subject but the whole video is very interesting.