Many 4* Bombers providing more upgrade skill set and surely can spice things up, but that doesn't mean 3* bombers are not good, i just 5* my Diana and i told you, 50% crit dmg is no joke, just look at their1,2,4 and 5 skill set and combine it with your team, check it if it's suitable or nah, even tho i'm new, i can tell 3* 'still' recommended