That's only partially true - the GDDRX you'd find on say a 3090 is physically very different than what you'd find on a strix halo or mac or vanilla ram. e.g. runs 4 voltage levels not 2 so that it can transmit twice the info per cycle
And then GDDR7 backed off to PAM3 and sends 1.5 bits per cycle.
There's a good chance [LP]DDR will use the same techniques once it gets into the same speed range.