The M1 Pro was not two M1s duct taped together. Their core configurations do not share the same proportions (8+2 vs 4+4).

You may be thinking of the GPUs? Each step in M1 -> M1 Pro -> M1 Max -> M1 Ultra represents a doubling of GPU cores.

Or you may be thinking of the M1 Max and Ultra. The Ultra is nearly just two Maxes.

Regarding your point about flexibility, it’s hardly unprecedented for the same core to be used on different processes.

Apple has at times contracted Samsung and TSMC for the same SoC. Qualcomm just recently ported their flagship SoC from Samsung to TSMC. Even Intel backported Sunny Cove to 14nm. And of course there’s ARM.