371A is -6db at 23Hz. It does have a potentially high cutoff as it is not intended to be an independently positioned sub but integrate as the bass section with The One series speakers. The high cutoff is to improve integration as a stack and allow flexibility in directivity. It has two drivers, the smaller one, by necessity, is at the top close to the higher frequency drivers of a stacked unit on top for proper integration. The larger driver handles the deepest base.
It’s 134lbs plus whatever is on top. The reactive force from the motor in the top driver will only marginally move the enclosure. Any resultant sound from that will be so far down it will be totally inaudible. The only concern is a mechanical resonance but Genelec is hardly new to making speakers. The "Newtonian" forces are relatively low and less than most think. The cabinet will only vibrate if poorly designed. Dual opposing woofers makes for much better marketing than improvements in sound. There will be things audibly vibrating in your room, but it won't be your speakers.
Many flagship speakers are WMTMW with a large woofer on top.