Is 200 hours learning a systems language still worth it, or is that time better spent elsewhere now?

Two hundred hours is two hours a day for a hundred days, which is a real commitment and worth budgeting honestly. Mine went into a language plus a small real project rather than a course, and the project was where the hours converted into anything. Rough split was 40 hours of reading and 160 hours of building and being stuck, and I would skew it further towards building if I did it again. Anything that is only reading evaporates in about a quarter.

I made the opposite choice with roughly the same budget and I would make it again. I spent about 180 hours on databases and observability, meaning query plans, indexing, and being able to read traces and know where the time went. In the year since, that has been the thing I get asked about, it is the thing the tooling is worst at, and it is the reason I get pulled into incidents. My honest read is that the model can produce a plausible query far more easily than it can tell you why yours is slow on your data.

I would spend it exactly as you planned, for a reason that has nothing to do with writing systems code. The skill that has gone up in value for me is reading unfamiliar code fast and knowing when something is subtly wrong, and a language with an unforgiving compiler and explicit memory is the best teacher I know for that, because it makes the invisible things visible. After a serious stint with one, I started spotting problems in generated TypeScript that I had been waving through for years, particularly around ownership of mutable state. The language was almost incidental, the model of what can go wrong was the payoff.

Nobody in this thread knows what the tooling looks like in three years, including the confident ones. Pick the thing you will still find interesting in month four, because that is what determines whether the 200 hours happen at all.

What I did wrong was spend six years spreading exactly this budget across whatever was new each spring. I have a shallow acquaintance with about nine things and depth in nothing, and the thing that finally made a difference to my work was going deep on one boring area for a year. Whichever you pick, the risk is not picking wrong, it is picking again in March.