Well, if the 16" MacBook wants to come out within the next half year, you're saying Apple has somehow boosted the GPU performance of the M1 chip by 3-4x within that time frame.
They'll either pull it off and it'll have horrible battery life, or you just have to be patient while they figure out how to do it efficiently, without sacrificing on the 20-hour battery life the base models just established.
The 16" needs its dedicated GPU performance. And I doubt Apple can pull it off while relying on just LPDDR4X. The 16" may need its own dedicated video memory or much faster unified memory overall.
While M1 is an impressive chip, it's also showing how much Apple is not ready yet for the 16".