Another example for me is Dave Gibbons. I was recently looking at several works he did after WATCHMEN, such as a story in MR MONSTER ATTACKS 1 (1992), and GIVE ME LIBERTY 1-4 (1990-1991) with Frank Miller. And to me, the quality of Gibbons' art in these and other later works have evolved and become better work than his work on WATCHMEN.
For me, WATCHMEN is completely an Alan Moore show, and Gibbons' work is not particularly exceptional or attractive, just functional. I look at WATCHMEN, and I see it as a very detailed script, and Gibbons just followed the script. And that many other artists could have illustrated WATCHMEN and done the same serviceable job, or even made the series far better!
To support my argument, compare it to Moore's THE KILLING JOKE. The panel layouts by Brian Bolland are virtually identical. The same 9-panel grid on virtually every page.
I frankly think Bolland is a more talented artist than Gibbons, but again, it's clear he just followed directions and didn't deviate one iota from Moore's script.
As compared to, say, Gary Leach or Alan Davis on MIRACLEMAN, or Bissette/Tottleben in SWAMP THING, where you see a great number of innovative page layouts and outstanding visual narrative.
So... Gibbons' WATCHMEN work wasn't so great.
