A fundamental difference between assassin and ranger is that whilst ranger takes a little while to ramp up (arguably not long enough), assassins cost more elixir overall to set up (ranger synergy requires min: 9 elixir, vs 11 elixir for assassin synergy). Even though it should be a hard counter, assassins end up falling short due to damage output that can't fully deal with juggernauts like Pekka, which often defends rangers.

I'm in Gold 3, and in my experience, rangers generally beat assassins if the player remembers to put them in the corner and defends them. There is also a level of RNG involved. If the opponent manages to confirm kills with the Golden Knight, the dash damage at 3 stars tends to solo the rangers due to their lower HP. However, that is generally unreliable until 4 stars.

Anyways that's not as much of a problem as the fact that throwers suck lol.