So what you are doing here is launching your intercept booster in a direction opposite the direction of the target object. When the dust hits the object it´s like two cars colliding head on, you don´t (generally) get one car speeding off faster than it was originally going. Both slow down

The dust that misses, is not doing near orbital velocity, so like the nice diagram shows, it falls back. (Remember an orbit is where you are constantly falling towards the Earth´s surface, but your sideways velocity is fast enough that you MISS due to the Earth´s curvature)

Making sure that the junk you want to take down is in the right spot for the intercept, that´s more tricky.

I like the Blasting, er ablating with lasers concept myself, and I think the electro motivc tether deorbit system is also worthwhile (Because, dude, electromotive tethers!! Drag the target down, or drag it up! all by cutting the Earth´s magnetic field with a conductor!)

In the short term for nuisance objects in LEO the suborbital shotgun here might well be worth it.

It’s probable, however, that the gas would disperse too quickly, or wouldn’t slow the debris enough to make it worthwhile, or it’d be too hard for the cleanup sat to get close enough with enough accuracy. Ahwell.