This thread has a lot of discussion about Wide Events / Structured Logs (same thing) being too big at scale, and you should use metrics instead.

Why does it have to be an either/or thing? Couldn't you hook up a metrics extractor to the event stream and convert your structured logs to compact metrics in-process before expensive serde/encoding? With this your choice doesn't have to affect the code, just write slogs all the time; if you want structured logs then then output them, but if you only want metrics then switch to the metrics extractor slog handler.

Futher, has nobody tried writing structured logs to parquet files and shipping out 1MB blocks at once? Way less serde/encoding overhead, and column oriented layout compresses like crazy with built-in dictionary and delta encodings.