Other mistake: At the end of the fight scene with the ooze men in the construction site we see the rangers flip in the air to regroup. Watch closely at the left hand side of the screen. There is some steam or smoke in the air which we see completely disappear instantly as Adam is going through the air. It doesn't dissipate into the air, it just vanishes. (00:25:50)
Other mistake: When Ivan Ooze gives out those slimes to the kids, that boy is at the very back of that big crowd. As Ivan Ooze starts giving them out, it switches to the boy and he already has some slime, but it would have taken a few minutes for him to get one. (00:42:00)
Answer: There's never a "point" to including a weakspot, by definition they are a flaw in the design that is either unforeseen or unavoidable. Maybe they could not find a way round it when building the robot, or any solutions simply created other weakspots.