Hmmh! Why do you need a JST to Molex cable, when you are only using XL-330s? Just regular X3P extension cables should work.
Are you daisy-chaining in series all your XL-330s? You could use these X3P hubs to parallelize your power and control circuits into groups of 4 or 3 XL-330s per “branch” out of the DXL MKR Shield - if your robot physical setup allows this procedure. That should help.
Come to think of it, I should use a current limiter on my robots too. Previously, when my XL-330 failed, it created a short so my XL-330 melted down at its DXL connector and also it was smoking!.
Also read this post, it has some other relevant discussions: