Updated with The Falcon and the Winter Soldier 1x02.
I know these weren't shown or mentioned, but how long do we think "new Cap" practiced with the shield? Surely not "never" as implied. Boom, you are cap, next day, expert with the shield. I'm thinking these episodes aren't actually "real time" (besides the flashback of course) as the timeline would apply, meaning it's only been a day or two for the whole 2 episodes. Should we assume John got the Cap title, then the shield (not SHIELD, haha) training, and now in episode 2, he's had the title for a few months? I guess it can be assumed his "regular" training was just part of his military training, but surely they don't practice throwing metal frisbies around. On the same token, we aren't supposed to believe that the same day that Falcon turned in the shield was also the same day that they gave it to John? Maybe my the time that he got the shield/ title of Captain America, by that point he'd already been practicing and secretly (him and the government) already knew he was the new Cap? Sort of like the US presidency (except the secret part); new guy appointed, but he waits (in the shadows.....) until the old guy leaves, then a few months later, he's in charge. Something like this:
Day 1: Sam gives the shield
Day 10: govt recruits John. "Hey buddy, you're pretty good with these military shenanigans. Wanna be the new Captain America?" "No thanks."
Day 30: "Hey is that offer still on the table? I think I wanna be Cap." "Yeah, sure. Take this shield. We made you an new uniform. The old ones we had were kinda stinky. We never washed em." "Yeah, sure, um thanks."
Day 90: "Hey guys, I'm really good throwing that shield thingy now. Wanna make it official?"
Day 91: "We have a new square-faced Captain America everybody!"
Something like that....
Also, I don't read comics (not even MCU tie-ins, movies/ shows are enough for me), so I don't know anything about any characters until I see them on-screen. So this Isiah guy. Assume it went something like this, right?
1945- Steve Rogers and Bucky Barnes are presumed dead.
Sometime between 1945 and 1951- Hydra finds Bucky the "one armed man", gives him some of their stolen serum, makes "bizarro Captain America".
Also sometime between 1945 and 1951- SHIELD (they are now SHIELD instead of SSR I presume) also finds another vial. "Oh hey guys! I was just washing my pants, and wouldn't ya know? When I went to move my pants into the dryer, I guess I had another vial of that "power juice" in my pocket. Wanna make a new Cap?" "HELL YEAH, let's use a black dude this time! Oh and also, let's keep this one a secret!"
1951: Hydra-brainwashed Bucky Super--- no Winter--- Solider tries to kill Issiah.
And I guess--- Super Soldier = Super-Serumed Good Guy and Winter Soldier = Super-Serumed Bad Guy?