I realize I mostly focused on the frontend side here, but you can easily see how backend dev is highly complex too (but that often falls under system programming too).
Lots of framework, in fact most of the runtime environment is not under your control at all (cloud services, for example). Complicated deployment and distributed patterns, often requiring many services to collaborate for a single functionality (DB, monitoring, cache, load balancing, backend itself, storage in just the simpler cases!). And none of this is something you can just plug your debugger into and hack away at it. Very similar to embedded in how I approach it.
Deployment is similar too, in that you will often have a builder system that creates artifacts than then get deployed asynchronously, resulting in heterogeneous environments at least for a while, with needs for proper API boundary design.
Seeing the parallels between both worlds allowed me to use CICD, blue/green, feature flags, data pipelines to the cloud, UI patterns from the then nascent javascript framework explosion back in the late aughts, when that stuff was almost unheard of in embedded environments. I scripted my jtag environment using rhino (javascript on the server, back before node came out) to collect and hot reload pieces of code, while being controlled in the browser. I made a firmware app store for midi controllers I was building.
Embedded UIs also highly benefit from knowing patterns from web frontend, because they are highly event based too, and really benefit from attention to detail (say, animations, error handling, quick responsiveness). At any point the user interacts with the device, through a button, a touchscreen, a sensor, UI feedback should be immediate and obvious (even if it’s just a LED turning on). Good web applications are absolutely amazing in how they achieve that (through CSS, through JS, with nice layout / graphical design patterns).
I think it really pays off to do both.