For the Amon thing, I guess what you said about range made sense but just because a character fails to dodge something at one point or another that doesn't mean they can't dodge it at all. Otherwise most fights in fiction would just be everyone dodging everything and never taking a hit. For example, Naruto can react to Sasuke's attacks but that doesn't mean he dodges all of them every single time. Also, Mako never "charged" the attack as we never see lightning building up in his hands so Amon wouldn't have known he was about to unleash it. In fact, the ATLA comics (which I guess I should've talked about more in my post) show us that lightning-benders
can use a weaker, non-lethal version of their lightning without charging which is pretty much what Mako did.
As for why characters would redirect it instead of dodging it, there's a few things to consider:
1. As I've said before just because you CAN dodge something doesn't mean you WILL. Otherwise why would a boxer punch at all if they expect their opponent to dodge it perfectly every single time. If a boxer had a technique to nulify a punch that required the minimum movement possible and would send it back at them would they not want to learn it?
2. Zuko did not learn how to redirect lightning to just avoid Azula's lightning. He learnt it to damage her with her own lightning. As Iroh puts it before trying to teach Zuko how to generate lightning (and later redirect it, once he sees Zuko can't make his own): "She is crazy and needs to go down. It's time to resume your training".
And as for the whole Ozai vs Zuko thing:
1. Zuko was likely caught off-guard by the attack. Fire-benders were supposed to be stripped of their powers due to the black sun (hence why Zuko was so confident in approaching his father in the first place) and the both of them were having a conversation. But Ozai got his powers back suddenly and attacked. The lightning was almost touching Zuko before he even started moving, so it was too late for dodging to be an option.
2. Zuko sent it back towards his father, giving him the change to escape. Dodging it would just prolong the fight. It's far wiser for Zuko to redirect it (something his father doesn't know he can do) and stun him than to dodge it and risk having his father attack more.
As for the Aang and Katara dodging feats:
1. Even though Katara was moving the water before the lightning was fired, we see the water is still moving after it was fired so we could compare their speeds (they're on-screen at the same time) to work out the speed of Katara's water.
2. As the lightning is already fired we see Aang land on the pillar, roll forward and then position his hand to redirect the lightning all before it hits him. How is that not a speed feat?