No, code traces are not just metrics; and while you can knit together something approximating traces from metrics, you'll quickly run into the reason why traces are a distinct thing. First, in a distributed system, you'll discover that you can't rely on clocks to get the timing of subsecond events correct. Second, you'll be contextless about code paths. So, you might independantly reinvent the idea of passing along a context - and now you're just making your own tracing system but without any of the benefit of building on years of existing discoveries in this field.

OTel does feel a little bit heavy, unless you're already used to e.g. New Relic, Dynatrace, etc. where you have to run an agent process and instrumentize your code to some extent; it's never going to be free to audit every function call! This is why (a) you sample down and don't keep every trace, and (b) unless your company is extremely flush with cash you probably don't run tracing in every environment. If you can get away with it just in a staging or perf test env you can reap most of the benefit without the production impact and cost.