I think you're looking at OTel from a strictly infrastructure perspective - which Cloudwatch does effectively solve without any added effort. But OTel really begins to shine when you instrument your backends. Some languages (Node.js) have a whole slew of auto-instrumentation, giving you rich traces with spans detailing each step of the http request, every SQL query, and even usage of AWS services. Making those traces even more valuable is that they're linked across services.

We've frequently seen a slowdown or error at the top of our stack, and the teams are able to immediately pinpoint the problem as a downstream service. Not only that, they can see the specific issue in the downstream service almost immediately!

Once you get to that level of detail, having your infrastructure metrics pulled into your Otel provider does start to make some sense. If you observe a slowdown in a service, being able to see that the DB CPU is pegged at the same time is meaningful, etc.

[Edit - Typo!]