hagak

They don’t shift the same way actually. Di2 uses a worm gear powered by a motor to move the derailleur, mech uses a spring under tension and a cable pull. Di2 can move much much faster with more precision and more force. For the rear it does not make much of a difference and even good mechanical can shift the rear under load. But the front is where it makes a big difference and the speed, precision and force allow it to move the chain under tension. It is also this ability that has allowed them to do synchro shifting since if they did not you would have to know to soft pedal on every shift since you would not know if the front shift would happen or not, but you don’t since the system can make those shifts with you needing to soft pedal.