Under no circumstances should any creature in this game function the way this butcher does. Completely ignoring minions is one thing, as broken as an ARPG can make it out to be. The fact that there is an extensive list of monsters that ignore minions, even when taunted is in an of itself bad game design, but to have a mini boss that not only ignores minions, but even has anti minion measures actively punishes people form playing an entire style that is built into the game.
Were the butcher act like many other bosses, and simply attempt to attack players from a distance, or begin focusing on those minions when completely surrounded, it would be no issue. Were the butch to simply charge on occasion or use an aoe to strike you as well as minions, fine.
But as it stands, the butcher is tried and true broken and needs to be temporarily removed from the game to be completely rebuilt, or permanently removed and simply retired from the franchise at this point.
The butcher should not have multiple, fast activating attacks that cause significant, long duration slows that are more or less unavoidable. It should not have a movespeed that overwhelms players even if they have a dungeon relic giving them the increased move speed buff. It should not have a no cooldown stomp that pushes all close range targets away and slow them. It should not have a charge that also stuns, and allows for an immediate followup combo.
Were any of these blocked or intercepted by the minions, or if the boss were to be taunted by minions, or if minions were able to body block or trap the boss, they would not have as much of an issue. But as it stands, the butcher is broken at a core, fundamental level. I mean, ALOT of this game is broken at a core, fundamental level, but this is simply another iceberg that is easily going to sink the titanic.