I pivoted a couple of years ago from SE to DevOps, and the latter has been far more complex in my experience.
Probably most importantly, my experience on DevOps has been a bit like hurried product management and software engineering work--I have to identify problems and opportunities to improve software development efficiency, uptime, etc and find/build technologies that solve those problems, and all of these technology choices are really complicated because they are interdependent. How you structure your CI/CD pipeline depends a lot on your orchestration platform (and vice versa). It also depends on whether you use micro services or a monolith, and whether your platform is mono/bi-lingual or fully multilingual. And unlike product management or software engineering, you have to deliver value in a much tighter timeframe (you don't get to spend a year building out a solution with budget and resources for user testing, QA, etc). Further, if you think the frontend web stack is changing fast, the DevOps world will make your head spin!
Regarding YAML, it's just the (currently popular) interface; it doesn't say anything about the amount of complexity. It was originally YAML/JSON because everyone thought it would be super simple configuration, but virtually every infrastructure-as-code (IaC) tool is moving away from YAML to something more powerful.
AWS has CloudFormation which began as JSON/YAML with features hacked on to support things like referencing other nodes in the document, defining and calling functions and macros, evaluating conditionals, looking up values in maps, etc. Now they're building the Cloud Development Kit (CDK) to let developers write IaC in languages like Python and TypeScript, because even the extensions to CloudFormation are insufficient (no ability to pass around parameters, pass structured data, perform computations, etc).
I don't use Terraform, but I understand HCL started out a lot like YAML but is also becoming increasingly powerful with each release.
Helm also started with YAML but is adding in Lua.
The argument that DevOps is easier than SE because it's just using tools created by SEs is silly on its face. First of all, those tools were _implemented_ by SEs but created by much larger teams, including product managers. Secondly, "SEs" are also just using tools created by SEs--compilers, interpreters, VMs, build tools, etc. Not to mention all of the tools and processes built and/or assembled by DevOps engineers.