Just how legit is using a controller to play MS?

There is no such thing as legit.

I concur...

 Huge Wall of Quotes

By signing up for an Account and using the Service, you represent and warrant that you are 18 years of age or over and have the right, authority and capacity to enter into this Agreement, or you are the legal age required to form a binding contract in your jurisdiction if that age is greater than 18.

There goes anyone under 18 who registered their own Nexon account.

You agree at all times to (i) provide accurate, current and complete information about yourself as prompted by our registration form or otherwise; and (ii) maintain and update your information (including your e-mail address) to keep it accurate, current and complete.

There goes everyone that provided false information, "including, without limitation, your name, e-mail address, birthday, gender, country of residence, state, zip code and ethnicity", as well as everyone who now uses a different email address than the one they signed up with, since Nexon doesn't let you change your email address.

We reserve all right to refuse to grant you or to terminate a username that: (i) impersonates someone else, including, without limitation, another user, Non Playing Character or Game Master ("GM")

There goes everyone who has part of the same name as someone else.

(ii) is or may be illegal or is or may be protected by trademark or other proprietary rights laws, or may cause confusion

There goes everyone who has anything resembling any brand name in their username, no matter how obscure.

(iv) is comprised of or includes the name of a popular culture icon, persona or media personality (e.g., "SpiderMan" or "TigerWoods") or religious deity or figure or your real name or surname

There goes naruto290586.

(vi) includes or is comprised of partial or complete sentences (e.g., "Youwillnotsurvive"), (vii) is comprised of or includes gibberish (e.g., "Akdnvprq")

There goes every single pineappling account in the game...

(viii) is comprised of or includes "Leet" or "Dudespeak" (e.g., OMGnewb, xLOLx, AFKbotman)

There goes n4ru7o239086.

(ix) is comprised of or includes any rank and/or fantasy titles (e.g., "MajorMark" or "QueenQiana")

There goes anyone with their job class in their username.

While using the Service, you agree not to:

# Restrict or inhibit any other individual from using the Service, a Cash Item (as defined below) or the Software, including, without limitation, by means of "hacking" or defacing any portion of the Service or Software;

There goes anyone who has to share a computer with a sibling that also plays MS.

Transmit: (i) any content that is unlawful, harassing, vulgar, obscene, hateful, fraudulent, threatening, abusive, libelous, defamatory, obscene, sexually explicit, or racially, ethnically or otherwise objectionable, or that could be deemed to be stalking or constitute an invasion of a right of privacy of another person;

There goes anyone who has ever defamed anyone else.

Engage in spamming or flooding;

There goes everyone in FM Entrance and PQ.

"Frame" or "mirror" any part of the Service without our prior written authorization;

There goes Hidden-Street.

Provide a link to any web sites that promote any product or any service;

There goes any MS player who's ever posted a link, anywhere, to anywhere, ever since they clicked "Sign Up" on Nexon.net.

Harvest or collect information about the Service, visitors to the Site or users of the Service without their express consent;

There goes any player that knows another player in RL.

Exploit errors in design, features which are not documented and/or bugs to gain access that would otherwise not be available or to obtain any competitive advantage;

There goes jumpshooters, jumpcasters, nearly all PQers ever (tracking, scouting, etc), laggers, and leechers of any sort (heh).

Reverse engineer, decompile or disassemble all or any portion of the Service, Cash Items or Software;

Oop, there goes Fiel

Disclose your personally identifiable information or any other person's or user's personally identifiable information (e.g., name, e-mail address, telephone number, age, address, etc.) on the Site or through the Service, or web sites or forums related to the Site or Service, including without limitation the Forums discussed in Section 2.3.

There goes anyone who's said their first name ingame, including to people they know in RL.

Ownership. Except for the personal information and content submitted by users of the Service, the Service and Software and all content included therein (including without limitation graphics, artwork, music, choreography, characters, character IDs, Forum IDs, account IDs, Cash Items and/or other items acquired or created in the Service, including through the Cash Shop) are owned by Nexon America or its licensors, and are protected by United States and other international intellectual property laws.

There goes anyone who's ever posted a screenshot or video, or uses any game images in a user-created avatar/sig.

I'd do more, but the rest is walls of text which I don't feel like processing.