While Grafana Agent uses less resources than Prometheus, there is more optimized Prometheus-compatible scraper and router exists - vmagent [1]. I'd recommend you giving Grafana Agent and vmagent the same workload and comparing their resource usage.
P.S. Prometheus itself can also act as a lightweight agent, which collects metrics and forwards them to the configured remote storage [2].
Here’s an article about this idea: https://datadrivendrivel.com/posts/rmrfprometheus/
You can substitute the Grafana Agents for OTEL collectors as well.