There's no limit to a Shinobi's progress.

[-ahhimane-]

I want to speak my mind and heart today on the manga "Naruto".

By far, we have seen shinobis who have progressed a lot, excluding their ways of mastery over their skills.

I would like to list them here. ( don't consider the order ) ( also, excluding the main characters and Konoha 11 )

Uchiha Madara
Hokage Senju Hashirama of the Senju clan
3rd Raikage
Senju Tobirama of the Senju Clan
Hokage Sarutobi Hiruzen of the Leaf
Tsuchikage Ohnoki
Medic Tsunade
Danzo of the Root.
Orochimaru
Jiraiya the Gallant
Uchiha Itachi of the Leaf
Kazekage Gaara of the Sand ( I could see his progress in the war much clearly than others )
Taijutsu master Might Gai

There's a reason I added the titles to the names of the few, for you to understand on what basis I listed them.
By watching these shinobis playing their parts in the manga, it explains (to me) how strong these shinobis are/were , by WILL, SKILL and MIGHT.


Now, If you want to add your list, you can post here.

 

[Matt]

Excluding the main characters this would be my list but maybe add Hinata in aswell due to her skill in the first part of the serious leading up into shipphuden she has grown alot

 

[Hyuga Prodigy]

The ones who should progress the most other than the main character would be the Supporting Character in other word (Konoha 11)

 

[inoyamanaka98]

Konohoa 11 are the only ones I have in mind that progressed the most

 

[KingHashirama]

Besides Naruto and Hashirama everyone has their limits.