I would expect the M4 being a newer generation of the chip to be faster than a M3, but apparently that's not what Apple did.
Is an Intel 10700K faster than a 12400F? The generations are different but the chips have vastly different capabilities and features.
M4 is the generation. The modifier modifies the generation. M4 Pro is an M4 with some extra pizzaz. M4 Max is an M4 with lots of extra pizzaz.