Heavy bombers role in conventional warfare, what's needed

I’ve been trying to find out what the average use the b-1 and b-52 contribute to conflicts current and past 10 years and what their priorities are. Is it the range and loiter time that is the biggest advantage, are they dropping 20 bombs a mission etc.
thinking if it’s range and Loiter time a cheaper airline conversion or similar cheap development with the necessary ecm integrated. If the future is large UCAV’s then heavy bombers (not including stealth bombers) become not needed. When looking at Iraq and IS battle it seems nearly all partners can deploy is fighter sized aircraft requiring lots of influght refuelling during long mission. It must be cheaper to have an a330 with modification for bomb bay. Thoughts anyone?