I prefer the idea of dual closers or not using your best arm in the closer role most of the time.
The best possible situation is to have a dominant lefty and a dominant righty and alternate them based on need. That will often give you really solid coverage of both the eighth and ninth innings, which significantly improves chance of victory.
An acceptable alternative is to only use your best arms if the deficit is one run, relying more on your secondary bullpen pieces if the lead is two runs or greater.
I don't believe in dedicating one guy to all save situations. It's too big of a waste of your most talented reliever, sending him into games with a 2+ run lead just because it's the ninth inning.
Using this tool, it appears that if the road team is down two runs going into the ninth, they have a 12.5% chance of scoring 2+ runs and a 5.5% chance of scoring 3+ runs.
https://gregstoll.com/~gregstoll/baseball/stats.html#V.2.9.0.1.0.0
Maybe, depending on the team and the order of hitters coming to the plate, I'd consider using my best reliever with a two run lead. I'd almost never use that reliever with a three run lead. It's likely he'd be more valuable in the seventh inning tomorrow night than the ninth inning tonight.