It's not PvP bypass. It's an armor effect that won't have effect unthil someone attacks you (in which case both players need to have pvp on).
I am not the one who removed it, just telling you what I see. We don't just ban or disable items just because. You asked the question and I gave you an answer. Done - Flim flam books | MineYourMind Community Done - Is magical wood banned? | MineYourMind Community Looks like this is where the issue was started: Implemented - Ban Flim Flam | MineYourMind Community
Ok, let's put it like this. 2 players enable PvP to play around. One of the players have FlimFlam on his armour. They battle, and one of them wins. For several HOURS after both toggle /pvp back off, the second player will have negative effect happening. Effects include, but are not limited to: Spawning charged creepers Dropping all items in your inventory(horrible if you happen to be in the nether etc) Teleport the player around randomly (see previous point)(done by faking an ender-pearl throw) Give negative potion effects. PvP was only enabled for a brief window of time, yet the effects last several times longer than said window. Now, maybe the player with FlimFlam forgot he had it on his equipment. Maybe he knew, and wanted to troll the other player, who doesn't know about FlimFlam. He'd only know that bad things were happening, not how nor why. In the end, it's cons heavily outweigh it's pros. (Only pro outside PvP being it's an easily crafted enchanted book)
There are also Witchery puppets that, while a lot more annoying and dangerous, as well as not requiering pvp to be swithced to "on" at all don't seem to get used against players. Not to mention PvP is super rare rn.