This reminds me of the Z-80, which replaced the 8080's 8-bit ALU with a 4-bit unit. Evidently FF recognized that it had no need to produce an answer in one cycle, because it would not be needed so soon, so why waste logic trying?
At the time, a 4MHz Z-80 ran about as fast as a 1MHz 6502, so that suggests opposite ends of that tradeoff range. 6502 had to do all its work in a cycle, but cycles were longer, so there was more time to do it in. Z-80 got half the work done, then the other half, with two more cycles left over for whatever.
This is what AVX2 used to do, too, working on 128 bits at a time. Probably when 3nm comes along, they will make it 512 bits wide if they can't think of and justify any better way use up their area budget allocation.
At the time, a 4MHz Z-80 ran about as fast as a 1MHz 6502, so that suggests opposite ends of that tradeoff range. 6502 had to do all its work in a cycle, but cycles were longer, so there was more time to do it in. Z-80 got half the work done, then the other half, with two more cycles left over for whatever.
This is what AVX2 used to do, too, working on 128 bits at a time. Probably when 3nm comes along, they will make it 512 bits wide if they can't think of and justify any better way use up their area budget allocation.