I think you're misunderstanding the change to Zintar. He will still reduce the melee attack of all enemy monsters by 1 point, unless that would reduce the melee attack to 0. At high-level play this will make no difference as almost all enemy monsters will have a melee attack of 2 or more. The change is strictly for lower level play where most monsters have a melee attack of only 1 and Zintar previously brings them all to 0 making them unable to attack.

Also regarding making balance changes, every good game does this on a somewhat regular basis (Hearthstone, Clash Royale, etc) and we will continue to do it as necessary as well. Creating a well-balanced game is the most important thing for us to protect the value of the cards.