Being Jinchuriki gives a person unlimited amount of Chakra, but this chakra is dangerous and can make anyone who use it go crazy.
Become Tail Beast is pure Chakra Energy, anyone who use it will gian unimaginable strength, but same time corrode by this strength as time goes by.
But Xin's situation is different, Ophis is strong, stronger than Otsutsuki Clan and even the Old Man Six Path.
Ophis is known as the Strongest Dragon in DxD, maybe the third strongest being if you listed, but even she is strong, she is also the most gentle of them all.
Maybe because of her small childish body, her mind also pure with calm and gentle personality.
And because she pure and white paper, she is more easy to please than a small kid so Xin get so many things from her.
Xin strength is thanks to Ophis power, she can manifest her power in the form of snake tattoo, which can increase a person's power after being consume.
She can create a snake tattoo which could bring out the full potential of Xin.
And because she is also a god, Ophis can bless people, granting them certain advantage and abilities, having no negative effect.
Xin got Comprehension, and Luck from her, this Talent is super rare even to this world, while Xin is originally a genius with 5x training speed that makes him powerful faster.
He also get Infinite Stamina, and Infinite Magic as he carry Ophis inside of him, this is one of the good traits of being Jinchuriki, you can get couple of ability of the Tail Beast.
Of course, as time goes by he can still get more, because Ophis is also trying to stop him form getting more strength from her.
Strength is the least thing Xin need, what he need more is comprehension and experience that's why he start training swordsmanship.
Ninja fight in this world is base on how fast you can cast your Ninjutsu and how much Chakra you have.
Only couple of people train their body and hone their natural talent, and Xin on the other hand know that if you train your body to limit, no Ninjutsu can hurt you.
"Hey Xin, you about to unlock one of the Secret Gear, you just need to train your Swordsmanship 4.'
'Thank you Ophis, you are great help.'
' Um.'
Even though Ophis is emotionless and expressionless, Xin can read understand her after spending time with her for seven years.
He know what Ophis want and want to express, their mutual understanding is better than Naruto and Kurama in 4th Ninja War.
Xin think her as little sister, he treat her as family and not a beast like those Jinchuriki, he also like her being clingy
when he spend time inside of the seal.