Bruh, not to be rude, please stop asking each class and start from a class that you like, get to level cap and enjoy the game contents :). You might discover what class suit you or your friends or your favorite class already sufficient.
now to answer your question.
if you want brief idea on playstyle there are a lot of videos of murmillo around, better check them out. most of the skills are close-frontal like peltasta/rodel skills, which makes requires positioning if you use swashbuckling. there are lot of skill to cast so it requires moderate-high usage of sp potion.
The burst capability comes from shinobi. Murmillo is used for +30% strike damage, immunity chance againts magic, and boosting low rank skills damage (doesn;t stack with clone).
As for comparison, a shinobi can beat doppel if boss have more than around 5m hp, pass and divine might are also synergy well with it.