I think the difference is that Backes was 4 years older than Landeskog when he hit the market and hadn't hit 60 points in his last 3 years in STL. His numbers declined in his final year, too. Landeskog's PPG over the last 3 years was higher than Backes' and he's on pace for 60+ points if this were a 82 game season. Most people, myself included, thought that Backes would have 3 productive years before his contract would get ugly the last year or two. If Landeskog signs a 6 year deal that would take him to age 34, which was how old Backes was when he had his last semi-productive year here. Landeskog is still in his prime.
Lucic was also a different animal because for the first half of his last year here he was lazy and a bit cashed out. It took playing with 2 young guys (Spooner and Pasta) to get him to move his ass and be productive. Sweeney moved him at the right time, because you could tell that he'd get an asinine contract from someone and it would be a disaster. Ironically, it was Chiarelli who gave him that contract a year later. Landeskog is more skilled than Backes and Lucic were when they hit free agency.