The M2 engine braking curve needs tuning for sure. Also, maybe the slipper clutch simulation is not fully correct yet.
As for the stock tyres... They are a long-standing problem that will have to be addressed sooner rather than later. There are a couple problems: 1) There is too much grip when the tyre is slipping at the max lean angle 2) However, when the grip is lost, it drops too quickly, making it almost impossible to control the bike The algorithms are correct, it should be a simple matter of tuning the tyres' physics data. I think that some mods already did a good job improving the tyres' behaviour.