Ok, this is mostly SPECULATION as I don't fight ROB mains, but don't characters that space well and aren't forced to approach good ROB counters? ROB controls space pretty well and can just shoot ya if you try to set things up, so I'm not sure if a character like Link has much clear-cut advantages over him, but what about Shiek, Falco, and Wolf? They can all return fire pretty quickly and IMO beat ROB out with their projectiles. On top of that they can take advantage of his so-called 10/2 and 6 o'-clock blind spots when they approach. All three can either combo him into oblivion, juggle him silly, and kill him off the top.
I can't vouch for what MILK did, but I'll be sure to tell him next time I see him. ;P
However, the focus point of the video is to highlight how dumb his laser is more-or-less. It's the thing I feel should be the most deserving of a nerf if the team ever decided to come back to him again. Anything else is probably fine, like I suppose you can argue his Dsmash is really fast, and I suppose ROB has far too many jumps on him for his own good, but I mostly want that laser gone.