Stupidity: Why would anyone put the controls for the reactor of the power station on a tiny circular ledge with no railings over a precipice overlooking a sea of lava? What sort of possible practical purpose would such a device have? It's not about the evil Empire cutting some corners and not caring for safety measures; here they had to consciously build a platform outside the rest of the structure, in a really impractical and dangerous position, that could get their own technicians killed anytime when they perform their routine duties on a curved surface barely wide as their feet.
Stupidity: In a throwaway comedy line, the Mythrol says that he still does not have vision in his left eye. For unexplained reasons that is the one guy that they take along for the dangerous base assault mission; a wimpy, obese, half-blind accountant. And for the whole mission he is quite a good shot, even (left-handed one at that, even). Cara is the Marshall and Greef the de facto 'ruler' of the town, who appears to be the biggest if not the only one of the planet; are we to believe the whole planet is so small that its whole defence is composed by these two people and there's not a single other able-bodied person on it? (00:11:30)
Suggested correction: The base was supposed to be practically empty, run by a skeleton crew. It was meant to be a simple, in and out mission and the Mythrol was just supposed to be their driver. He goes with the group inside, against his better judgment, because the lava tide will be coming in soon. It is never stated that the four members of the team are the only able-bodied people, they simply believed that the four they bring would be enough. Which as it turns out was completely accurate, given the fact the team succeeds even with the base being full of stormtroopers. Also, you don't have to be a stereotypical tough guy to be a good shot. There's plenty of people that aren't soldiers and are far from in good shape that are perfectly capable with a gun.
And that are also blind in one eye? I figured that the lava tide was just an excuse to bring him in - no such tide is shown to affect the area, even if the mission takes them longer than they anticipated.
You say in your mistake that the blind in one eye comment was meant to be humorous. No reason to believe he was being completely honest. But yes, it is not unheard of for people with limited or even no vision in one eye to still be a good shot. It only limits your depth perception and peripheral vision. No reason you can't hit a target right in front of you with only one good eye. Regardless of whether or not the lava tide coming in was a true statement or just an excuse to get him to come in, it isn't a stupidity mistake that the group brings him in. These mistakes are not for actions by characters you would not agree with were you in their shoes. This category of mistake is for an action so daft it defies logic, such as running back into the building with the killer you just escaped.
"I'll bring my pudgy accountant to my base infiltration mission, he has a speeder bike" doesn't sound exactly logical, no (other than the fact that he's a funny character and helps making the episode entertaining). If he was supposed to just be their driver and then an extraordinary circumstance such as their speeder bike being destroyed forced him to abandon a "Keep the speeder running" (as Mando says en route - in a typical trope, they are discussing their roles and basic mission objectives only when they are already well on the way and have zero scouting or tools) plan, it would have followed some kind of logic, but that is not what happens, they drag him in. When do you ever see in a robbery/heist movie the characters tell their getaway guy "come on in, we could use one more guy with a gun actually, forget our only escape mean"? By any logic he'd just slow them down, he even just showed them that he's not any good at picking a lock.
It doesn't rise to the level of a Stupidity mistake. Bringing him isn't an action that is so stupid it seems unbelievable. He doesn't even appear to be as much of a hindrance to the mission as you suggest, they seem to operate just fine with him there.
Of course they are the good guys and it all works out in the end and it made for a fine episode, but for all we know and they know, they dragged a non-combat trained and physically unfit accountant to their commando mission, the fighting part. It's already a big stretch that the magistrate and the marshall of a whole planet have to resort on that guy of all people for a getaway driver role (he's not even portrayed as being a great pilot, since Cara drives the vehicle they will escape with: he's literally there because he's got a bike and he's an indentured servant), but it sure seems unbelievable they brought him - inside the base - all of a sudden with no story justification about it (which would have been really simple) and contradicting the original plan.
