If hyper-miling is the top priority then I believe laws of physics favor the ID4 D mode. Regenerative breaking can never be 100% efficient so conversion of speed to battery charge and then back to speed will be less efficient than coasting and losing less speed. It has been shared in some of these forum topics somewhere in the past that this was part of the rationale in setting the D mode default to coast rather than to automatically slow with regeneration.
This is correct. When spending energy ( gas or electric) to invest in increased kinetic energy ( speed), there are efficiency losses. When braking ( gas or electric) there is a loss of kinetic energy through friction. Friction brakes are used in ICE cars to convert kinetic energy to heat through friction. EVs can regain some of the the kinetic energy to add energy to the battery but there are losses through the transmission, the motor/generator ( heat and friction) and in conversion of electrical power to chemical storage in the battery.
Every time there is a conversion of energy, there is a loss ( chemical to electrical, electrical to mechanical, mechanical to electrical and electrical to chemical. There are losses when charging your EV car ( this does not apply to ICE cars).
The most efficient way to drive ( ICE or EV) is to minimize your investment in speed. Use as little as possible to gain or maintain speed in the first place. Then, coast as much as possible.
Drive like you have no brakes
and you will experience the most efficient use of on-board energy ( gasoline or battery charge).
Having said all of this, yes in the city, when it is not possible to be maximizing coasting, regen can be helpful as one is forced to be hitting the brakes often. But even then, the payback is limited.
EDIT: After all, we are talking about hyper-miling here.