I think Custom Jr is a good weapon in most cases, especially on Tower Control. I have played Custom Jr in S+, and lost very few matches, and in addition have played 3 League rotations in twins where I exclusively played Custom Jr, where I got 3rd, 6th and 7th place. It is foremost a support type weapon, more so than the vanilla Jr is even. You should go on the app, and see how much turf they covered in each ranked game, because I almost always cover 1500-1700p of turf, although generally my kills are also decent because of assists.
I consider the Custom Jr, with specific gear more so, a tactician type weapon. Most of your kills come from assisting teammates, or throwing out Autobombs, or Ink Storms, that do the killing for you. It is easily possible to see people who do not take such an articulate mindset to the game, and are detrimental to your team, but I think it is flawed reasoning to assume that every single Custom Jr is going to be a detriment to your team, before you see them in action.