They were prominent names, but there's absolutely no way of telling how Minato compared to Raikage or how proficient Itachi's capabilities were in terms of Genjutsu without actually encountering them. C made a statement explicitly comparing Base Raikage's reactions to Minato's despite never ever encountering or seeing Minato in battle. Likewise, Ao likely never encountered Itachi yet knew that only Itachi was capable of accomplishing what he did. Itachi wasn't even as famous and was only known for Amaterasu and Tsukyomi, not his general genjutsu capabilities.
I understand your point with the bold, but C nor Ao really had much intel on Minato and Itachi at all yet made detailed comparisons, so I hardly see why this couldn't apply to Hashirama at all. To be honest, I just find it intellectually dishonest that you think someone whose at the level that can at least fight alongside Naruto and Sasuke and reflect a Sannin's abilities at such a young age only be considered comparable to a 5 year old. I also find it intellectually dishonest that you choose to actually believe that 5 year old Tsunade had refined chakra control above even expert medical ninja. There's absolutely nothing at all that suggests what you're claiming is logical. Hashirama boasting about Sakura having as much strength as a 5 year old? Yeah, that's totally believable.
The scan above shows three kumogakure ninjas squaring up against Minato and his team. Future Raikage A, Killer Bee and someone else. The scan also shows that was their first time of encountering Minato but they had heard about his exploits. Few scans after, they kind of fought experiencing first hand Minato's speed. Add that to the fact that reports on the clash would have been given to the Kage at the time, it would be easy to deduce how Cee who was portrayed in his few panels as being analytical was able to make a statement about Minato's speed.
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From the scan above, because he has seen Sasuke's use of Amaterasu(eg Raikage's speed) he's able to deduce correctly(as confirmed by Black Zetsu during the fight with Sasuke and Itachi) that Sasuke is actually better skilled than Itachi in using Amaterasu(eg Minato's speed) even though he hadn't encountered him.
As for the Itachi claim, he was a rogue ninja and was listed in the Bingo book. I'm sure Genjutsu was listed under his skills there.
This shouldn't have been argued as long as it has tbh. If you don't know a person, you can't have an hypothetical opinion of said person. If I gave you names of a singer from Spain and another from Uruguay, you won't be able to tell me who is better because you probably haven't heard of them and never encountered them.
The only Tsunade Hashirama knew when he made that statement was 5 or 6 year old Tsunade. He can't make an hypothetical opinion of an adult Tsunade he hasn't seen nor heard about. Kishimoto probably meant something else but unfortunately, this is how it was portrayed.
