You sure can, easily, as I have been repeatedly. The objective record shows that the two players in question perform among the elite players of the league
Except that they don't. Thornton is #21 in PPG (and #5 in the RS) and Marleau is #44. As SJgoalie says, if that is elite, then what are players who are top 10 or top 5? Super-mega-ultra elite?
Plus, a lot of those players, especially around Thornton, like Anze Kopitar and Toews, have been better defensively for a longer period of time than Thornton.
while facing significantly harder deployment than other elite players
Toews gets his team's hardest matchups (at least according to Chicago fans). Kopitar get his team's hardest matchups. Same for Datsyuk, or Bergeron.
If you look at zone starts, Thornton is about par-for-the-course relative to other star players in the league, and that is not including T-Macs preference to have Thornton take defensive-zone starts (or Quenville's preference to have Toews take offensive zone starts).
Plus, Thornton is blessed with some of the best teammates. Marleau the same if you look at other players in his position.
The problem is when you don't recognize that the opposing TEAMS were superior but the Sharks did lack individual elite talent or play. They lacked the TEAM construction to place the TEAM in a position to succeed. This is mostly a question of DEFENSE which is extremely difficult to build to an elite level without high draft picks.
Dave Bolland is hard deployment? Jared Stoll is hard deployment? Even Jeff Carter, is hard deployment?
I feel like some fans want this perfect scenario where JT will have two superstars on his wing, with two studs on defense behind him, vs. an injured ECHL fourth line. That's not going to happen. If JT gets Marleau and Heatley on his wings, backed by Murray and Boyle, he needs to flatten a matchup of Bolland, even if Bolland is backed by Keith. If he gets the opportunity to face Jeff Carter, he needs to take advantage of that.
Think about what a player like Kopitar did in 2014. With Gaborik and Brown on his wings, without being tied to Doughty, he owned many of his matchups, including against the Sharks.
You can always say that Marleau had to "drag" Nieto on his line, and Stuart/Demers/Braun were uninspiring..but Marleau and Couture were both outplayed by Nieto. You have to set higher standards when other players around the league are achieving a lot more with a lot less.
Lastly, I will add that the Sharks primary issues the past 5+ years has been SCORING. The Sharks have had one of the premier offensive d-men in the league during that time in Dan Boyle. Thornton has had Dan Boyle with him on the PP, and often as his linemate. He's had wingers like Marleau, Heatley, Cheechoo, Guerin, Bell, Setoguchi, Pavelski, and Burns. The only time he has ever remotely had to drag "crap" around come the playoffs was with TJ Galiardi and the few times Ben Eager played on his wing.