Tsunade is mid kage level.with maybe two exceptions,NOBODY has gotten that strong without bloodlines/bijuu
Ohnoki-has a kekkai touta,the most advance elemental bloodline in the series
Ay-unknown bloodline that gives his family extremely strong bodies and bijuu level chakra.
Mei-literally only uses elemental KKG
Gaara-his sand manipulation is from shukaku.debate that all you want it's mangafact you still retain power from beasts after losing them.
Kakashi-sharingan is a kkg.uchiha or not,he stilled used the sharingan religiously.
Lee-a fair example although he's not nearly tsunade level.
Need I continue?
Strong ninjas not from a mentioned special clan:
Minato being one of the strongest and his clan was never said to be special. A and his father, they trained to get strong and the first time we see A he's lifting weights. Bee, at a young age he was closest to A in strength to be his partner and his base own Sasuke and Taka with no Bijuu influencing the fight in the beginning. Hiruzen clan wasn't special, Hiruzen was the only Kage level and he surpassed the Senju Hokages that came before him. Kakashi graduated from the academy at 5 and became Chunin at 6 all with his own skills before getting the Sharingan; in fact he's weaker because of it since he had to learn to use it and he learned earth and water element to be able to copy jutsus other than lightning ones and he said it's hard to learn just one element. Gai isn't from a special clan and he's a Jounin that Itachi was even cautious of. Kurenai isn't from a special clan and she became a really skilled genjutsu specialist that only Itachi with his Sharingan was as good as. Orochimaru isn't strong from his clans. Jiraiya isn't strong from his clan. Konan isn't strong from her clan. Kabuto wasn't as strong as Kakashi in part 1 for his clan.
Shall I go on? None of these ninjas clans were mentioned to be strong and the ones whose clans were never mention only show how their clans had nothing to do with it. You try to over look A, Oonoki, Gaara, and Mei for what they can do? They all trained to learn their jutsus, especially Oonoki and Mei who had to learn to use their elements and if the regular ones are as hard as Kakashi said then the KKG are even harder. Their clans were never mentioned so that's their own power and not from being in a clan so that still counts. The Raikage's are all muscle heads, don't count their training as a clan ability when it was never mentioned or implied; they have some crazy training is all. Gaara might have retained Shukaku sand powers but it was Gaara's own ability that allowed him to use it after losing the Bijuu and he shown to master those powers extremely well.
Sakura has always been commenting on having great chakra control; medical ninjutsu, super strength, yin seal are all based on chakra control. Tsunade even said that Sakura has come a long way in medical ninjutsu in just 3 months. Tsunade compared Sakura to Shizune who's been her student since she left Konoha many years ago
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. Chiyo compared Sakura to Tsunade and even said she could surpass her. Sakura even learned the Yin seal in her 3 years if training with Tsunade when Shizune who train with Tsunade much longer couldn't even do. Sakura strength was said to probably surpass Tsunade by Hashirama himself. She might not have overall surpass her but she's only 17 and a 54 women who doesn't train isn't going to lengthen the gap any so Sakura will surpass her in time.