That's just my take, feel free to disagree.

Unless you have a degree in Psychology and can accurate measure if a player could have a mental block I'll disagree.

in S5 they did have an easier group though

No they didn't lol. At best in your argument, it was even.

but in S4 they were even IMO

No again. C9 was 2 AA from taking Blue to Game 5. TSM lost 3-1 and that included a troll game from White.

Anyone that actually watched all games knows TSM was the better team, hell Meteos, a player on your dam team, said TSM was the better team, it's just they got an easier group. C9 had to beat out fucking FW to get out of groups, RNG was much better than FW. Also, SSG crushed C9 3-0, TSM took a game off SSG in super dominant fashion and had an extremely close game 2. When will people understand placement =/= actual team strength, especially because of the format Riot uses for worlds.

Outperforming doesn't mean that you were better, it simply means you went further, which C9 did. That isn't up for debate.