That would be an essay, but in short:

Grafana is fine to get to a selfhosted basic install. But once you try to actually connect logs, metrics, traces in selfhosted context and perhaps sprinkle some otel in...that sht gets out of hand very fast. It's modular in a way that seems like a win but once you start connecting stuff it starts adding complexity not ease.

Signoz...still pretty early in exploring this and so far it's acceptable, but it too relies on a mix of query languages incl the competitors promql so some panels support it other seem to not to?

The entire thing just seems bewildering to me. Not gonna say "why is this so hard" because I genuinely thing smart people are genuinely trying here...but there result just isn't great.