User blog comment:Njalm2/Nanja's Classroom: Weaknesses/@comment-24384232-20160525220103/@comment-3403804-20160525222339

Well, Jacks of all Trades are largely limited by just how good they are in a field, and they're naturally weak to specialists. Their abilities are also frequently lesser in terms of scope than a true dedicated user, or at least they should be, so as to preserve the central design.

Beyond that, true Jacks are defined largely by a lack of big weaknesses, because they usually have few actual strengths - as they're very skill-intensive to utilize effectively. If they've got specific weaknesses, it's probably based on their preferences and fighting style, which does differ from character to character.

One might be overly strategical, and thus lack the ability to follow through, or perhaps possessing few good ways to finish off an opponent in a pinch, another might be very focused on providing multiple forms of utility, and might lack actual defensive or offensive options. A third might be a raging hothead who simply wishes to do the most damage, and therefore eschews defensive and utilitarian abilities in favor of bigger stronger techniques.

Essentially, with Jacks, weaknesses depends upon the direction they're taken, as it's not unusual for them to have something of a semi-focus on certain talents or tactics. For instance, Byakuya is a fan of blending magic with swordplay, and often employs a catch and crush, or cripple and terminate style of fighting. Where he utilizes Kidou to either immobilize or severely inconvenience someone before finishing them off with the rest of his skillset. Its a brutally efficient fighting style, which epitomizes exploitation of offered openings.

Creating meaningful weaknesses for them generally involves taking them in a specific direction; and then ensuring that there are some realistic "gaps" here and there.