But they come out right next to the planet. You can exit the jump at the edge of the solar system, micro-jump in another direction, then micro-jump back towards the planet. The gravity well stopper only happens at short range; it's not like you have to exit at the edge of the solar system and burn the entire way in.
Not to mention that it's a planet. It's not a warehouse. It's thousands of kilometers wide, and its orbital space is a few orders of magnitude roomier than any combat arena humans have ever fought in. Even without bringing hyperspace into it, the idea of a few ships being able to "blockade" that entire immense volume is beyond preposterous. You'd need to surround the whole planet with a cordon of thousands of ships. Or, more plausibly, just build a ground outpost or use a squadron of aerial ships to defend the specific location on the planet surface that the enemy is trying to reach.
There's also the fact that ships in orbit are not just hovering in a fixed position. They're racing around the planet at high speed like cars on a racetrack, except in three dimensions and with gravity pulling them in toward the center of the track. There are countless trajectories that could be taken to get to the surface.