No need to ban the bastard sword, because it's not part of D&D 5e yet. D&D Wiki is mostly full of things made up by random people on the Internet — the Bastard Sword you link to is some random person's homebrew. You would have to choose to add it to your game, not ban it.
Is it balanced? Meh, doesn't matter. You don't want it, so there's no reason to think about it further.
Avoid D&D Wiki. Use official rules references instead.
Unless you're specifically looking for homebrewed content ideas, you should probably avoid D&D Wiki like the plague, since it has so many problems. Actually, even for homebrew, it's notorious for being full of things with massive balance problems that aren't worth your time.
You can get the official Basic version of the rules from Wizard of the Coast's website at that link. You can also get the content online at one of the more respectable 3rd-party sites that republish the 5e System Reference Document (“SRD”), such as 5eSRD.com. WotC also runs D&D Beyond as their own 1st-party digital online version of the rules.
For rules and game material, the Player's Handbook, SRD, Basic rules, and/or D&D Beyond should be your first source, not some wiki or a Google search. You'll save yourself and your players a lot of headaches.