Because most stats and their values are balanced around the fact that they only serve to buff the player. Extend those things to minions where each and every benefit from them, especially chance-based effects. Especially those that are solely meant for damage(ie. knockback, stun, etc.) And you will undoubtedly find unintended able broken behaviors.
And the main reasons it deletes pure summoner is because with no real wall between the player and minion stats, means that no matter how i build for my minions my own power is getting strong and im even futher incentivised to be hybrid and attack myself. Like if my attacks do 100 dps when my minions deal 20k dps, theres no point. But if i do 10k dps when my minions deal 20k. Theres no point to being pure summoner. Especially when its not like you are even making any interesting build choices to enable this behavior, put on damage gear and swap to your own weapon and profit.




