[KaVir]

Emphasis mine. It's true if any of those you are marketing your game to are existing mudders. Also note that "better" is a subjective term - you might think your client is great, while someone else might think it stinks. If people have the choice then they'll use what they prefer, while if they don't they might decide to give your game a miss entirely.

You can still offer them a custom client without excluding other clients. Forcing people to use your client won't make your mud any more appealing to newcomers, it'll just raise the entry barrier for existing mudders.

You're creating a mud which doesn't target mudders?