Fighting games are heavily based on the characters, it's the whole point of every franchise in the genre. It's more than just about cool designs, moves, and abilities however, it's about how all those things come together. This leads to some characters being in a higher tier and some being in a lower tier of the game.
Pros are constantly looking at the tier lists of games to ensure that they have the best chance at victory. Some of these tier lists can be interesting, with characters being farther up on it than one would think and others being far lower than players would have guessed.
10 Jin Kazama - Tekken 7
One would think that a character that has been the main protagonist of the series ever since the third entry to the series back in 1997 would be a top pick, but in the case of Tekken and Jin Kazama, you would be wrong. By no means in Jin the worst character that you could pick in the game, but he is definitely not as high as he is in the series story and how he is pushed would make him seem. Jin is at best a mid-tier pick but most pros put him in lower-mid tier and even low tier. At least his Devil form is pretty good.
9 Ryu - Street Fighter V
Speaking of fighting game protagonists that aren't the best picks. Ryu from Street Fighter should probably be one of the best picks in the series considering how popular he is and the fact that he is pretty much the mascot for the whole fighting game genre.
Ryu actually hasn't been that good in the Street Fighter series for a while, not being one of the best picks in Street Fighter 4 but in the most recent entry, Street Fighter V, it's even worse with Ryu being one of the worst picks in the game's roster.
8 Swamp Thing - Injustice 2
Swamp Thing is one of those interesting characters that if someone was asked if they had heard of, there is a decent chance that they would say yes but if they were asked if they know anything about the character beyond his name, they would probably have nothing to say. That's too bad as Swamp Thing is a really interesting character with cool powers and stories, unfortunately, neither got shown off when the character made his appearance in Injustice 2 where he was low tier from the start.
7 Shao Khan - Mortal Kombat 11
There's an interesting dilemma that comes to developers whenever they decide to make a character that used to be a boss playable. This usually happens in sequels and developers have to balance the expectation of the boss character being powerful with the actual balance of the game, to make sure that the character is not overpowered. It seems that Netherrealm Studios had a hard time with this as Shao Khan, the most notable big bad of the entire Mortal Kombat franchise was really weak as a playable character in Mortal Kombat 11.
6 Mega-Man - Street Fighter X Tekken
Mega-Man has had a rough few years recently (more like a decade). The Mega-Man franchise is seemingly on indefinite hiatus after the franchises creator and Capcom had a very public breakup and the spiritual successor, Mighty No.9 didn't do so well. Mega-Man's appearance in the Street Fighter X Tekken game wasn't good for the character either. It jokingly used the terrible box art version of the character from his first game and made him incredibly weak.
5 Uriko - Bloody Roar
Bloody Roar is a fighting game franchise that has fallen out of the minds of most gamers and even hardcore fighting game fans. This makes sense as the last game in the franchise came out all the way back in 2003.
The first game introduced us to a cool concept and an interesting boss design. The game was successful enough to warrant a sequel and this time around the first game's boss, Uriko, was made into a playable character. Similarly to Shao Khan, playable Uriko is nowhere near as strong as she was when she was a boss and in fact, was made into a joke character like the previously mentioned Mega-Man.
4 Mii Fighters - Super Smash Brothers Ultimate
Having your own created Mii become playable in multiple Nintendo titles was a pretty good choice by the legendary game company. The player can create a character that looks like them or an abomination that should have never seen the light of day. This was done predominately in two games, Mario Kart and Smash Bros. The first title was ok, as the character doesn't matter too much but in Smash Bros the different types of Mii fighters failed to make a real impression
3 Yoshimitsu - SoulCalibur 6
Yoshimitsu is a really interesting character, as he is a mainstay in two different fighting game franchises. Yoshimitsu started out as the first of many guest characters in the Soul Calibur franchise, coming over from Tekken But Yoshimitsu stayed around as both games are made under the same publisher. Yoshimitsu has been in both franchises for a while and has shifted between the different tiers for each of them but in the most recent entry to the Soul Calibur franchise, he has basically become a joke character.
2 Vegeta Blue - DragonBall FighterZ
It's hard to think that the strongest iteration of the Prince of all Saiyans, Vegeta, would be one of the lowest tier characters in a game but that's just what it is in Dragonball FighterZ. Each version of Vegeta isn't really that good, with his base form probably being considered the best but his Blue form is for sure the worst. The strange thing about this is that you will still see Blue Vegeta selected a decent amount of time because his assist is actually pretty strong, but as a character himself, not so much.
1 General RAAM - Killer Instinct
In a similar vein to Shao Khan and Uriko, General RAAM is a boss that became a playable character in a fighting game. What differentiates RAAM from those characters is that he isn't a fighting game character, he's a guest character to Killer Instinct from Gears of War. RAAM was one of the last DLC characters that was added to the game but he doesn't get across how powerful and menacing the character was in the original Gears of War, in fact, RAAM is considered the worst charter in Killer Instinct.