Phaleg is just a reaction test at this point due to the power creep making the S rank easy to hit if you can react. The fight doesn't really check positioning or planning either.
If you're just trying to assess your own skills, 4-man Persona trigger is a lot broader in coverage, and the Varuna story fight is more fair of a duel boss (healing, can avoid instead of iframing, can fish for counters on swords, etc) while still being easily accessible. Don't pay too much attention to the exact times you get, but ask yourself whether there's anything you did that you did that you could have improved on. Those two fights have a lot of ways to shave time off that are applicable to other bosses. Precasting, blind spots, chain counters, all sorts of things. Plus they both push you hard on defense, but let you heal instead of resetting the whole thing.