Is my packet competitive enough to be selected for 17C?

Best way to find out is to submit the package.
Always give someone the chance to tell you "NO".

Hey, I too am currently in the same shoes you are, reclassing from 19D to 17C (Combat job to a Cyber job).

In Short:
Talk/Network with people, learn on your own and gain certifications that can be shown on paper, contact Retention NCO, and build your packet.

Long:
What I have done so far is I have been in contact with my Retention NCO, discussed ways to improve chances of my packet being accepted by talking with my units S6 NCOIC (of whom is a 25D) and other relevant MOS's, because networking and gaining connections in the proper channels can go a long way.
1.) My Retention NCO has given me the link to the Fort Gordon website to obtain the 17C reclass packet that contains templates and forms (7 files in total), then she is now assisting me in obtaining a Top Secret clearance and other information about current requirements for this MOS specifically (i.e GT/ST scores, clearances, rank, etc).
2.) The S6 NCOIC has recommended taking CompTIA classes (A+, Net+, Sec+) in that order, to build my resume (to improve packet acceptance), and has assisted in contacting others (such as a 17C who also re-classed) that would shed more light on the situation.

My plan:
Gain all 3 Certifications in CompTIA, obtain a Top Secret clearance, and continue to study/learn in my off time.
A few ideas to do/learn: Learn various OS's and their respective command line/shell [i.g Kali Linux], be fluent in at least one programming language [I suggest Python, and shit like HTML is not a language], network/talk to others that know subjects regarding cyber, computer/web/software development, types of attacks [Phishing, MITM, Honey Pot, DDOS/DOS, forms of Viruses, etc]. -I can go on all day on what to learn, but bottom line is start somewhere and don't stop learning; intuition and desire is key.

Conclusion:
Don't be afraid to submit a packet with what you have, worst case is it gets pushed back, and you might have to extend a year for stability till it does get approved, just keep trying. Also, your re-class packet is like applying for a job, you have whats basically a resume (a memo) that you need to fluff up to basically sell your self, so include all your certifications and experiences (no matter how small or big, every penny helps).

I hope that helps/clarifies your question, and Anyone that has further questions, please don't hesitate to reach out to me.

If you have the right ASVAB scores and can get a TS/SCI with Full Scope Poly, it's possible, but keep in mind that the 17C training period is over a year and it is not easy. Be sure you know what you want before you commit.