Servus Matthias,
I think nothing is wrong with your setup and you can still use it. Here are some thoughts from my side.
If you want to use loki for logs you better use promtail. Otherwise stay with hepipe.js or if you are mainly interested in kamailio
and rtpengine logs you can use heplify with the flag -m SIPLOG especially when you have a lot of logs (>10k per sec).
With this heplify will capture them on UDP Port 514 and send them to heplify-server. It will look for warning and error
logs and give you a special metric with hep type 112 in Grafana. Very helpful to detect failures.
You can use heplify for SIP and RTCP too. This has the advantage that you can use the -hn flag and set a node name.
As far as I know you can't do this in rtpengine. With this you will get RTCP metrics based on the host heplify is running.
We for example use multiple sipwise carrier blades with 7 proxies and it helped us to identify packetlost for some proxies.
But since you only use SPCE you can stay with RTPengine and captagent.
About Asterisk. Just use heplify for SIP and RTCP. It's a single binary with some flags to setup. For logs use promtail or hepipe.js.
BR,
Eugen