Sorry but your own source contradicts that:
"When I was looking at the Starscream prototype that Takara Tomy had made, they told me, "We don't mind if you make significant changes," so this was an opportunity to put forward various proposals."
Original Takara developed Prototype:
Note that the tail fin and fuselage overall section used to be much smaller (as in flat) and attached to his legs just like the G1 toy. Kawamori made that section thicker in order to improve the realism of the jet mode which he did remarkably well and succeeded. However for no reason other than his own preference, he decided to take them out of his legs and hang them of his hips for a 'Samurai swords' type look which conforms more to his own design style.
The decision of attaching the tail fins to the hips is the main issue that I have with his modifcations, not taking the original release execution into account, I am happy with his modifications except the tail fins in robot mode. They should have stayed on the legs.