The minion hitbox is meaningless because it is an issue with minions position lagging. (Ever seen minions suddenly sprint or magically jump forward? That was the problem in that clip.)
The hit on Gragas was caused by how his hitbox is effected by using his dash, and therefore more of a glitch on Gragas's hitbox in his dash, so again meaningless.
The hit on Shaco makes perfect sense. The animation for Thresh's hook is based on the width of the scythe blade, even on the side that the scythe isn't currently on. Mentally flip the blade, and its pretty obvious that the blade would indeed hit Shaco. Working as intended, no problem there. Again, meaningless complaint.
On the Irelia toss, once again, the blade clearly contacts the edge of Irelia. Making it inside Thresh's hitbox.
If your complaint is that it looks weird for something that hits at the edge of it's hitbox to jump to the center of the champion, that is an animation issue, NOT a hitbox issue. If your issue is actually with how wide the impact point of the Thresh hook is, none of these videos made it seem particularly problematic because it was more often glitches of bad programming related to other issues that caused the problem than Thresh.