"most accomplished" is correct and usable in written English.
You can use it to describe someone who has achieved a lot. For example, "John is one of the most accomplished musicians in the world."
Glover, now forty-one, is certainly the most accomplished tap technician living — probably the most accomplished who ever lived.
Frampton rates this as his most accomplished performance.
This could be Villeneuve's most accomplished film so far.
Beare considers this to be his most accomplished work.
Mr. Dine's prints are among his most accomplished works.
Forgiveness is afforded to Rooney in the knowledge he is England's most accomplished and potent threat.
Responsibility also might be dawning on England's most accomplished forward, Wayne Rooney.
Michael Cragg of The Observer called it Beyoncé's "most accomplished album yet".
He erased Daniel Murphy, the Nationals' most accomplished hitter, with a pop-up.
Waiting to bat was Matt Holliday, St . Louis most accomplished hitter.
