Updating this because my rankings most certainly changed after Season 14. I'm also going to include 4th place semi-finalists prior to S7 this time.
23rd: Cutter (S5)
Cutter and Tali both hold the record for the worst chefs to ever make it to the top 10, with Cutter easily being the worst semi-finalist in the history of MasterChef. I'm convinced they kept him to ensure the final three being Courtney, Elizabeth, and Leslie.
22nd: Alejandro (S11)
Same reason as my first list, although I will give him credit for improving a lot after the top 10.
21st: Samantha (S9)
Same reason as my first list.
20th: Noah (S10)
Same reason as my first list, even though he basically had a free ride to the top 10 due to how inconsistent and weak most chefs were this season (I'm probably one of the few people who thought S10 was a weak season).
19th: Reagan (S13)
Even though Reagan is among the weaker semi-finalists, I'd much rather have her in the finale over Jennifer, who was inconsistent through the competition and was saved numerous times.
18th: Lee (S1)
Same reason as my first list.
17th: Sheetal (S1)
Same reason as my first list.
16th: Suzy (S2)
Again, basically had a free ticket to the final four due to the lack of talent in this season.
15th: Christian (S2)
Same reason as my first list.
14th: Krissi (S4)
Easily the most hated chef, but even then she did have some talent and stood out on a few occasions.
13th: Emily (S12)
Same reason as my first list.
12th: Becky (S3)
Same reason as my first list.
11th: Frank (S3)
He's among the most talented chefs this season, I just don't think he's as good as the other ten, especially considering that this was an early season.
10th: Murt (S14)
This might be a surprise to put him this high up, but Murt in my opinion, is probably in my top 5 most improved chefs in the history of MasterChef. He started off from the bottom in the first few challenges, then out of nowhere, began dominating in the kitchen, similar to Alejandro in S11 (despite his improvement being overshadowed by the better dishes), but on an even bigger scale. I think him being in the finale would've been entertaining, but I don't think he was ready to win.
9th: Stephen (S6)
Same reason as my first list.
8th: Nick (S6)
A standout chef in a pretty forgettable season, I put him above Stephen simply because I felt that Nick would've had a better chance at beating Claudia in the final three challenge.
7th: Shanika (S12)
Same reason as my first list.
6th: Jessie (S4)
Same reason as my first list.
5th: Tanorria (S7)
Same reason as my first list.
4th/3rd: Leslie (S5) / Wayne (S13)
On my previous list, I put Leslie above Wayne because of his insane track record when it comes to pressure tests, but I realized that Wayne had just as crazy of a track record, ever since dodging elimination in the top 13, he's been winning challenges like crazy. He won the fish challenge in the top 11, won the patio grilling challenge in the top 9, won the wall challenge with Grant in the top 8, and led his team to victory during the restaurant takeover, as well as being on the winning team of every team challenge (excluding the tag team challenge, but I don't really consider that as a traditional "team challenge"). I honestly can't really decide who's better, so I just decided to tie them both.
2nd: Cate (S8)
On my previous list, I put her as the best semi-finalist due to her avoiding being in the bottom throughout the season, but she's been brought down to second place due to one other chef's surprising elimination.
1st: Rebecka (S14)
When I watched S14, I could've sworn that both Rebecka and Michael were locks for the finale with the third spot being up for grabs for basically anyone in the top 10. She's had a similar run to Grant, having a strong performance to begin with, and even after struggling later on, she managed to bounce back in the wall. If this were any other season, she would've won, hands down.