Those mazda's are kind of cheating when they say they have 16 to 1 or whatever, the fuel is directly injected into the cylinder after the piston is coming back down and the cylinder pressure is not so high as well as cam position being manipulated to increase or decrease overlap and retarding the intake valve timing to reduce cylinder pressure. At part throttle when cylinder pressure is reduced by the throttle restricting airflow then it may be injected closer to or even before TDC butt again, cylinder pressure is not as high under those conditions.

Motorcycles run high compression as a result of a typically very straight shot of cool air to the cylinders with very minimal if any heating of the air as well as small bores that tend to ward off detonation and very large cams that bleed off pressure. The individual runners also tend to run much smoother with a very large cam than multiple cylinders running off a common plenum with a huge cam, the cylinders are not interfering with each others air/fuel charge. Remember too that 1.9 inch stroke is not moving the piston any faster at 14,000 than a 3.8 stroke at 7000, twice as many cycles but nearly equal average piston speed. It is hard to compare a motorcycle valve train to a pushrod engine, the cam is usually pushing directly on a lash cap/tappet thingy with no pushrod or rocker arm weight to deal with at all and none of the weird harmonics that need to be dealt with that are associated with them.