That level of permanent reduction for everything from Fact or Fiction to Comet Storm
You can win in one single blow dealing not only enough commander damage but also enough infect damage thanks to Grafted Exoskeleton depending on how many equipment and auras you have attached to a creature
But when you have five untapped Vampires, you can gain control of a creature and vamp it up at instant speed
Secondly, being aggressive with a commander like Jirina Kudro is a good way to punish players for clunky precon mana bases or inconsistent starts, both of which are issues for some of the other precon decks
Feed it artifacts to build up energy and kill, it's very Fallout-esque, and fits nicely into commander
Rather than being better than flying, horsemanship is basically just a different version of flying that isnt forwards or backwards compatible