first off - you can't and shouldn't equate RoR line of work (monolithic architecture) as definition for all of full stack dev work out there. More often than not, full stack dev work encompasses microservices for your backend and a separate frontend app running their own frameworks (e.g. Javascript + React for frontend while Python + flask for backend).
What you ought to say probably is that you are enjoying web development but in a monolithic environment -- nothing wrong with it, I just wanted to clarify concept in your mind.
Secondly, I too transitioned from being a DevOps engineer for 6 years to working as a Developer. My take is: Money depends on the job - both can command more money than the other but I would bet that if you are thinking about contract work, then DevOps would probably pay you more.
In terms of competition, there is more 'intense' competition for Dev jobs -- at least here in Toronto, Canada. Why? Because as a Developer, you are expected to know things like data structures, basic algorithms, big frameworks (spring boot and react are pretty large frameworks in their rights). Then, there is increasing usage of coding tests before you even land an interview.
You don't do coding tests typically for DevOps jobs and even if there is, it is not intense -- you don't have to do SQL, you don't have to do OOP, etc.
Also, DevOps tooling are getting so advanced that majority of work is getting pretty simplified -- your 'tech stack' may only consist of yaml files (albeit for different tools) along with some python 'glue'/automation code. Heck, even in depth OS knowledge is not that critical now for majority of DevOps jobs ever since docker and k8s stole the scene. Finally, even the whole part about 'assisting and building CI/CD pipelines' and 'creating CI/CD relate framework for Devs in organization' and 'debugging build failures' and 'strategizing Git structure' is quickly moving towards Developers themselves doing all that so you are just a fancy tool admin in many cases. This ultimately will cause you to loose out on many modern proper software development skills and practices.
Up until couple of years ago, knowledge about a major cloud provider (e.g. AWS or Azure or GCP) and knowledge about usage of the SDK / creating templates would have been your saving grace and would have made you stand out -- but now, Devs are doing that more and more and they are more capable of doing so not because they are necessarily smarter than DevOps folks, but because of plethora of info available on internet plus such abstracted/simplified controls available via these Cloud providers in terms of SDKs and highly usable web consoles.
Finally, one thing that I felt personally regarding the job situation was that, in every company, the ratio of dedicated DevOps folks to developer would STRONGLY be in developer's favor. Sure, there is more competition for Dev roles but there are a whole lot more jobs in the market for Devs as well as compared to DevOps.