...the fact that their best works (in your opinion) were on other titles does not necessarily mean that their Wolverine work (like e.g. John Byrne's work on the FF, Alpha Flight, Superman etc., or PAD's work on Spider-Man, Supergirl, Young Justice etc.) was to sneeze at or that they couldn't write a good Wolverine.
Also, wouldn't writing a good "old school" Wolverine be the opposite of "jumping the shark", so why should adding something new to Wolverine even be a necessary criterion? Finally, the Claremontian Wolverine is to a large extent John Byrne's baby due to his co-plotting during the CC/JB run. It was due to Byrne's influence that his fellow Canadian Logan gradually took centre stage and developed his familiar personality (Len Wein wanted to make Colossus the star of the book and Dave Cockrum obviously favoured Nightcrawler).