The Mk 16 was designed to cope with a "wider range" of body weights and sizes. Whereas the older seats had quite a narrow margin of userability.
The technology used in the rocket can sense what it is pushing out and adjust thrust to give the same end result and envelope of operation with very small (female) and very large (porky males) (OK and porky females) occupants. The seat also has unique sizeing capabilty (stretch) to accommodate the different heights of occupants. It is a great bit of kit and extremely capable. It takes ejection seat design to a new level. It is also extremely comfortable. I know, 'cos I have sat on one.
Canopy jettison or through canopy is a matter of design. Through canopy tends to be quicker but does have its downside (MDC splatter etc). Type of a/c and operating environment and capability also have a bearing on which system is used. VSTOL a/c tend to have a through the canopy system due to the possible high sink rate of the the a/c in an emergency and the ability of a rocket assisted canopy jetison system being degraded by that situation.