The Blues went to the Stadium of Light knowing only a win would keep alive their chances of securing continental football.
However, they were silenced by the Black Cats who got their goals through Trai Hume and a own goal from Malo Gusto.
"It was a disappointing end to the season," McFarlane told Chelsea website after the game.
"We should be finishing a lot higher up the league. For me, with this group of players, the talent we have, we should be in the Champions League. We've been too inconsistent at times this year and it's ultimately cost us.
"The feeling in the dressing room is obviously of disappointment. We wanted to win today and make the best of a bad situation and get into the Europa League.
"We weren't able to do that. We didn't get the performance we wanted, or the result.
"I can only speak on my interactions with them over eight games or so and I have no qualms or desire to question their mentality in those moments.
"I know we didn't win every game, but they gave us everything every single day. I could ask no more, and we just weren't able to get over the line in some of the games that mattered."