I've struggled with the closer role for a while. I've used a configuration like deanod where I have 3 SuA and no closer. Until I found a pretty decent relief pitcher with 14 stamina and 60ish durability. a guy like that isn't able to throw a lot of innings anyway. I use him as my closer and he's been really good. I think that's the only way I'd use a closer is if the guy has sta/dur problems.
Otherwise, you should have at least one LR, and as an alternative to LRB and/or mopup, I like to have a SuA or SuB guy who can eat innings ie. has HIGH stam/dur.
Current bullpen config
Spahn: LRA, SuA, SuA, SuA, SuB, SuB, closer
Caneco: LRA, LRB, SuA, SuA, SuA, SuB, SuB