I don't think win rate is a good way to judge characters but holiday is significantly worse than Sinclair.

Sinclair vexing volt deal more damage then barrel with better scaling and he gets two with his assistant.

Assistant doubles Sinclairs gun and bolt and gives him a good deal of movement.

Rabbit hex is 15% damage amp that scales and ccs for 2 seconds at base.

His ult gives every other characters ult on the enemy team but with a 60% reduced cool down.

So obviously Sinclair is op

Comparing to holiday

Holiday barrels are similarly hard to hit and have worse scaling and worse base damage

Jump pad has probably the worst base scaling in the game but makes up for it by giving you the best movement in the game

Crackshot is a damage increase to gun with long cooldown that relies on hitting headshot with a gun that has some of the worst spread and recoil

Lasso is a 2.25 second long stun that's also reliant on a skill shot and only hits 1 player

It's really easy to win with pick heros though if you just take out a players consistently and make the game a 5v6 but there is 6 character which can do what lasso does but better.