You'll be fine without a mid-range driver.
Some swear you want a mid-range driver. Others swear you don't want to double your crossovers by needing two. Others swear no crossovers at all and use only a singe full range driver. Let your ears decide for you.
BTW- I have heard the 170 classic and the M-22 in the same room same equipment and the 170 has a better mid-range, control on highs, and details IMO.