Cass was able to navigate the votes better than Karla then win final immunity to get there. Like Jeff mentioned to the jury during questions that they need to keep in mind that the reason many of them are on the jury is because someone felt they were a threat to win the game. There are many people over the history of Survivor that were great players that never won. Karla and Jesse both could have beaten any of the final 3 I think but the key to winning usually comes down to can you outwit your biggest competition when it matters, can you make fire in a fire making challenge, or can you win the final immunity challenge. Some of it is just luck to get to the end really. I get irked when you have some bitter jury members that try to make the final 3 all about them and how they feel they deserve to be there over them. Sorry but we are 43 seasons in now and if you haven't figured by now that once you are out that is it and no one cares if you think you deserve to be there instead. That's another thing about the jury is that every season how they pick the winner depends on their mindset. Some are bitter and won't vote for someone because they were the main person behind many of them being voted out while others care too much about the social game and ignore how someone navigated votes and won immunities at key times to avoid being voted out.
To me this season all 3 were pretty much a wash for the immunity challenge part as all 3 won nearly the same number so it came down to owning their strategy and how they played the social game and Gabler did that better than Cass and Owen did IMO.