What about those Deathstars that are quite cost efficient? Deathstar does not have to equal expensive. Take the ubiquitous Inquisitor with Death Cults Assassins in assault transport; it can come in extremely cheap and can be quite hard hitting. That squad routinely rolls TH/SS termies, even fairly equal numbers of them. The unit can come in around the 380pt mark, which puts it on the top range of "normal expensive unit" and on the bottom end of the "eggs in one basket range".
Sure you can blow up the land raider; but to do that before the unit inside will be moved up the field a damaging amount of distance, you will have to throw a disproportionate amount of firepower at it. This unit is not nearly as expensive as what you would consider a regular deathstar, so using it as a fire magnet is reasonable all things considered.