Design is always a important matter! But true speed in operating lever guns is ALWAYS a function of practice, practice, and practice! You can often out shoot a better design with the competence that comes from loading with your eyes closed until it is second nature. (same with DA revolvers)
The major flaw with the 1860's Henry design was the magazine raceway was a channel instead of a tube, and a hard bump could cause it to pinch closed enough to impede the follower, for firing or reloading! Also with centerfire ammo, letting the follower slam into the stack of ammo after reloading has been known to cause chain fire explosions at Cowboy shoots.
My personal favorite of the design family is the '73 (& '76) [mine is in 44 Special]. Steel frame, loading gate, but so much smoother than than the Browning design ('86. '92, & '94) or the Ballard/Marlin Design. (very numerous!) This is based on low pressure rounds, when it comes to smokeless and magnum pressures, FORGRT IT! [I own several Browning and Marlin designs and like them too] But for a 15 or 20 round combined string of fire, loading gate take the cake!
For a single round reload, dropping one in the open bolt is pretty darn fast if practiced!
Ivan