They do have reload vehicles you know.
Plus what good is a fully loaded HQ-17 if the ship it is on is sunk?
As mentioned by the preceding posters, the landing ship shouldn't be operating outside of fleet air cover and air support should clear out as many known anti-ship batteries as possible.
Initial spearhead should serve to maximize fighting defensive positions on the shore, that means marines and ground fighting vehicles.
Landing forces need to push forward and take over a port or airport to maximize the ability to land reinforcements.
HQ-17 is not reloading under these circumstances, and a reload vehicle has no fighting value.
Your costing is the final nail, if you are afraid of the landing ship being sunk by a cruise missile, stick the HQ-10 w/ datalink on. It's the same cost as an HQ-17. The fact that this is an additional cost should not be an issue because this is a matter of national survival.
AEW will detect cruise missile launch and if the ship is in danger, then HQ-10 will engage it.
HQ-17 can land and engage threats further inland in the way it was intended to and a slot on the landing ship in the initial assault would not be wasted on a vehicle with no fighting capability.