Lee Barkell's biggest success as a pairs competitor was a win at the 1986 Nebelhorn. Going on to coach Olympic medallists and world champs...
Doug Leigh was the junior silver medalist at the 1966 Canadians. Between Elvis and Brian alone, he's clearly more successful as a coach. Similarly, Frank Carroll was a national junior medallist in 1959 and 1960.
Igor Shpilband was successful as a skater - 1983 world junior dance champ, but definitely more successful as a coach.
Don Laws' highest placement was 7th at the 1951 worlds. Scott Hamilton brought him a lot more success.
Definitely Nobuo Sato who reached 4th at the Worlds, but never won a major international.
Galina Zmievskaya - I don't know anything about her competitive results (if any), but Petrenko and Baiul were definitely successful under her...
And similarly, I know nothing about Rafael Arutunian's results a competitor (except for Wikipedia saying he started skating at 7 and was coaching by his early 20s.
Carlo Fassi had some success (winning Euros and medaling at Worlds), but between Peggy Fleming, Dorothy Hammill, John Curry and Robin Cousins... he's probably one of the most successful coaches ever.