Nonsense. Nieminen has almost always faced top calibre opponents and I think only once or so has been higher ranked in the final. Ditto for Benneteau.
You may want to compare to someone like Tursunov who is 7-2 on ATP finals, but his opponents have mostly been clowns.
The ranking of the opponent shouldn't matter much when it wasn't a problem for these guys in the matches they won to get to these finals.
No matter what you say there's no excuse for Nieminen with a sample of 11 matches - the only guy he managed to beat was Ancic who was a clown in finals himself - losing to the likes of Arthurs, Moodie and Dupuis.