/gamerule combatVersion ---- changes combat mechanics

version 1.9+ saw a major change in combat mechanics, and the new experimental combat snapshot has even more changes. Some people prefer 1.8 combat over the current combat, and some will prefer current combat over experimental snapshot combat.

/gamerule combatVersion    should allow you to switch between 1.8, 1.16, and experimental mechanics so that you don't have to specifically play on the older versions.