From General Sorin (might be from others as well, didn't bother to look)

"If you own the Return to Hoth expansion, the Imperial player can choose the "Bombardment" Agenda set when building his Agenda deck at the start of a campaign."

My question is, does this wording imply that Bombardment is only supposed to be used when playing the Return to Hoth campaign, and not Twin Shadows or the core campaign?

Or is it just because his maps require the RTH tiles, and you couldn't play the mission without the expansion content?

I assume the later alternative... as otherwise the wording would have been "When playing the Return to Hoth Expansion" rather than "If you own". I assume its not just the tiles, but possibly also figures and possibly other rules from the expansion.

Makes sense. Just didn't know if they meant for certain things to be campaign specific for balance purposes

Kayn Somos was the same way. His mission required the Twin Shadows expansion for one of the tiles.