They should recheck the area surrounding where the pings were heard. There wasn't enough mapping done there. It is highly possible to have a distorted frequency towards the end of battery life.
NTSB simulation plots based on Great Circle Track where assuming the FMC would guide the autopilot system to fly. But with the aircraft had made a few turns, most likely the pilots had reverted to MCP direct input to the autopilot system where the track is magnetic be it on TRK SEL or HDG SEL, is subjected to high magnetic variation further down south. Thus, when the magnetic track being plotted would be a curve towards East. But a curve cannot satisfy the handshakes. If the handshakes are correct, this magnetic curve line can be "straighten" by lifting the tail end Northwards while maintaining all the handshakes relationship with the satellite position.
Just imagine the capital letter "T" with the handshakes numbering from the left to right, the position of the satellite is at the bottom of the vertical shaft and the letter T has fallen 90 degrees to the your right. Now you have handshake no.6&7 at the right hand bottom, you are lifting the "T" pivoting the bottom of the shaft to the satellite position. Try lift it until no.7 handshake ends up in less than 5 degrees variation. Then you will agree they have been looking too far down all this while.
Welcome any expert comment.