Stadium as it is, locks you into your hero choice. There is no counterswapping, which is what the Draft System is there to prevent.
Introducing the Draft System in Season 18, is going to make Stadium a very miserable experience for quite a lot of people honestly.
Not only is the roster in no way large enough to facilitate 4 heroes being banned, but the fact that you’re locked into the hero that you do pick for the entire match, completely bypasses the need for a ban system, which was introduced to curb counterswapping, something that isn’t present in Stadium.
Stadiums entire thing is “buy items to counter the enemy”, not “Swap your hero to counter the enemy”.
Bringing in hero bans can, and will, just cause one team to be at such a major disadvantage for the entire game, that it wont be fun, and wont even be a challenge at all. It defeats the entire point of using Items to build to face the enemy, when you’re on a hugely unfamiliar hero with so many different playstyles available now.