Im surprised there's still no "trace" view of pipeline execution, especially with how prevalent DAG pipelines have become. Somewhere on the internet I found this handy jq oneliner that will convert a pipeline into a format you can drag and drop into chrome://tracing/ to figure out where your bottlenecks are

  curl "https://${GITLAB_URL}/api/v4/projects/${GITLAB_PROJECT}/pipelines/${GITLAB_PIPELINE}/jobs?per_page=100&private_token=${GITLAB_TOKEN}" | jq 'map([select(.started_at and .finished_at) | {name: (.stage + ": " + .name), cat: "PERF", ph: "B", pid: .pipeline.id, tid: .id, ts: (.started_at | sub("\\.[0-9]+Z$"; "Z") | fromdate \* 10e5)}, {name: (.stage + ": " + .name), cat: "PERF", ph: "E", pid: .pipeline.id, tid: .id, ts: (.finished_at | sub("\\.[0-9]+Z$"; "Z") | fromdate \* 10e5)}]) | flatten(1) | .[]' | jq -s > "${GITLAB_PIPELINE}-trace.txt"