For my money, Thranduil is the best option—not necessarily to kill Bolg, but to be in that helping-Thorn/parallel fight position. Because seriously, that conflict between Thorin and Thranduil needs a resolution.
Unfortunately, I suspect this never occurred to the PTB because they don’t see Thranduil as a person. More a device. And his purpose in AUJ and DOS was make Thorin look like the most put-upon underdog, who is just treated so unfairly.
But if they’d treated Thranduil like the significant supporting character that he is, developed that conflict between him and Thorin—and all it implied—then keeping Thranduil on Ravenhill (alone or with his army), provides optimal fulfillment/resolution to what came before.
Even without development, though, Thranduil going up to Ravenhill sooner just has more oomph than whatever they think they’re doing with Legolas.
Point being, just about anybody would’ve made more sense than Legolas in fighting Bolg. Okay, Alfrid is worse; zombie-Smaug is worse; Galadriel or Saruman are worse; Gandalf is … comparable? But I’m pretty sure that if Bolg had tripped over Bilbo’s unconscious body and impaled himself on his own pointy armor, it would have been more satisfying than what we got with Legolas.
I cannot comprehend what they were thinking.
(Actually, putting Bolg down in Dale to be killed by Beorn or Dain works really well.)