You need to learn your spacing. Ragna's 5B beats out Jin's 5C clean, Jin has hitbox on his cape on startup, you have plenty of time to outpoke him. Seems to me that your blockstrings are not rock-solid. Seems to me that you're impatient and probably extremely obvious with your approaches. You don't need to: run up -> 5B every single time. Mix it up: run up 2/3 of the distance you would for 5B -> AirDash > crossup j.B, etc etc. Seems to me that your Jin opponent plays like me, he must be overusing 5C to beat incoming run-ups and relies on DPs as anti-airs even when 2C would work.
You must know that you outpoke Jin on all grounds, don't be scare of him. I hate y'all, Ragnas >_>. Also, double jumping is your friend. You can approach by running, jumping, keeping barrier guard on, ultimately blocking that DP, then doing dj.C. That causes a lot of trouble to us, Jins. Our only ground move that has lots of vertical range is 2C, which is very slow and can be seen miles aways (DP C is a no brainer, nobody would dare using it in such tight circumstances.) Bait his DPs with far airdashes that allow you to barrierguard by the time you enter his DP hitboxes. If close enough, even DP A can be punished.
Also, learn to anti-air with 6A, it will benefit you in the long-run (and short-run too in fact!). Jin's j.B/j.2C totally get owned by Ragna's 6A. Jin's j.B spam does not exist, it's too easy to beat out.
1. Practice your spacing.
2. Learn rock solid blockstrings and mix it up.
3. Add more variety to your approach, being unsafe can be safer than playing safe when your opponent knows your narrow gameplan. Bait DPs like they're cookies.
4. Use 6A to beat our aerial approaches, just watch out for air iceblade. They're pretty easy to look out for, so don't react early to his ADs.