The move off datadog was painful and I'm not convinced it was worth it, but that's how it got "optimized".

I’m also curious about this. The indexed spans costs a lot. How do people usually filter them and base on what?

depending on how deep you want to cut costs, the best way to optimize is to simply send them less data.

at my last place we relied heavily on APM traces in prod and kept the sampling rate relatively low. you can add metadata and send custom trace entries to take the place of most log entries. likewise the most valuable metrics could be derived from APM data easily enough. we kept shipping the must-have logs and custom metrics but their volume was surprisingly low once the noise was gone.

also, I don't think I'd ever let datadog slurp everything from AWS cloudwatch again. the amount of pure useless noise there far outweighs the value. a few targeted collectors from services like WAF and AWS SSO were all we really needed in the end.

TL;DR: be ruthless and cut cut cut. you might be surprised at just how much is never used. also, avoid letting datadog integrate with lambda or ECS, since those come with a per-unit cost which is fairly extravagant.