Maybe you're right. However, this should not about individual persons / projects... this is more about that I'm still uncertain, why so many experts cannot get this thing right by just working together finding a suitable solution :-) There must by more than one way of solving this.
I'd argue that he is right about the fact, that the "driver" (libinput) should not send "simulated" events, that are not really there. Whereas the cursor movement should defintely stop the scrolling behaviour, the driver is not the place to care about this, I think it is more a compositor / window manager thing, but I'm not an expert.
However, if he would implement an opt in solution (2 config options) for lets say:
libinput.simulateKineticScrolling=1
libinput.kineticScrollingSpeed=0.22
a lot of people would be really happy, but this probably is a really dirty hack.