Minato died before he reached his prime power, he died at 24 appearantly and skilled ninjas usually reach their prime 30-40. You can say his prime would be during Naruto's birth since alive>Edo. Also at what point during his fight with Juubito did you expect him to be completely still to gather natural energy? He was too busy saving Naruto and Sasuke from Juubito to helping Sasuke and Naruto hit Juubito with their Enton FRS with Edo Tobirama, then giving Naruto chakra via Yin Kurama while FTG everyone to teaming up with Naruto to fight Juubito, to getting his chakra absorbed and rendered unable to fight until his chakra replenished.
Minato's skills with SM is where Pein Arc Naruto's skills were. Naruto was told he couldn't use SM in battle without comrades buying him time to be completely still to gather natural energy and balance it with his chakra and SM only lasted 5 mins at that time if I remember right, or until you used all of the Senjutsu. Edo Minato said it takes too long to knead Senjutsu as it did for Naruto, and he couldn't maintain it for long as Naruto couldn't. That's where fusing with Ma and Pa toad come into play, a Edo which is dead shouldn't be able to fuse with them. Also Edo Minato couldn't use the benefits of SM as SM awakens the body and you can't do that to a dead body. Toad SM users don't use senjutsu to enhance their strength, speed, durability, recovery rate, ect... The senjutsu powers up their body as Pa toad told Naruto how it awakens his body in many ways. An Edo body wouldn't get those powerups unless they actually used the senjutsu chakra to enhance their capabilities as Tsunade's/Sakura's enhanced strength focus chakra to a single point and release it or A's/3rd Raikage Lightning armor enhance their speed.
Itachi's only time we can say he didn't have his illness is when he was 13 but Obito knew of Itachi's illness and needing to use medicine to stay alive so part 1 Itachi and Part 2 Itachi are sick. If you want to choose a less sick Itachi then you'll have to remove Totsuka blade and Yata mirror since that Itachi would have to be before part 1 took place and for all we know a Itachi didn't have those weapons until the 3 years time skip. Also by that logic you can say Minato's prime is him living the 16 years and got much stronger so he can be in the same time period as Itachi and everyone. Minato is already strong enough to fight 2 strong and skilled Kage level ninjas at the same time and leave A with believing no one could surpass Minato and leave Bee trembling at the mention of Minato.