Reserve card additional users are free, And they are receive complimentary SC access'
Delta Sky Club Access
Delta SkyMiles® Reserve Basic and Additional Card Members receive complimentary access to the Delta Sky Club when traveling on a same-day Delta-marketed or Delta-operated flight. Reserve Card Members traveling on a Delta partner airline flight that is not marketed or operated by Delta may access the Club at an exclusive per-visit rate of $39 per person, per location.
The vanilla Amex Platinum charges $175 for each "authorized user".
It is the $175/year Delta Reserve Additional Card that is being referenced here (unfortunately, Amex card T&C's aren't very explicit). The DL Reserve Amex card has exact same $175 fee for an Additional Reserve card as the regular Amex Plat card for an additional Plat card. If you don't want to pay fee, there is a no-fee additional card option for Reserve cardholders and these additional cardholders just get a regular Delta Plat Amex card that doesn't include comp lounge access.
