You're looking at them too literally.

Infection: We see a transformation of a human into a fighting machine capable of incredible destruction, and the human's will is subverted. Meanwhile delenn and sinclair are both going to have their own radical transformations, and Sheridan is going to become that fighting machine. His will gets subverted as well 'damn me for agreeing to it and damn you for asking'. We also see that this is a universe where humans are ripe for being taken advantage of by the enemy and their tech. It's the 4th episode. We haven't learned anything about earthgov or the technomages or anything at this point, but he's giving us the context with which to understand what's coming.

Believers: The child is terminally ill. Franklin saves him, but it doesn't take. Even with the best intentions and the necessary tech he still fails. You can win and still lose, which is basically the whole setup for crusade. There are many reasons aliens don't ask outsiders for help. We see it again with the Marcab, but the difference is how delenn and Lennier choose to accept that there will be loss. This is the lens JMS wants us to see the narn and the centauri through. They are both dying races and how they accept it or not is extremely important for everyone.

TKO: It's about determination and acceptance, but it's also about why we do things. This is the battle John goes through with the shadows and the vorlons. What Garibaldi's friend is being asked is 'what do you want' and 'who are you'. He starts out with the first question, and gets rebuffed. When he ultimately answers the second and things go better for him. But crucially, not because he obeys anything. It's because he's strong and independent and true to himself.

I get that you don't need to rewatch them because you have the context. But I wonder if I wouldn't have viewed the rest of the series the same way without these campy, heavy handed storied. He really slams home the message and I think that's on purpose.