Metrics are useful. You don't pull the trigger based on metrics alone, but it's not like they are garbage.
If you are looking for aged domains, or finding sites to guest post on, and you have a shit ton of domains to filter, then what are you going to do? Looking at each one and making a manual assessment is going to have diminishing returns. You need a starting point and metrics are an excellent place to start.
While not 100% accurate, they're accurate enough for the initial analysis, or in other words 'statistically significant'.
Once you have a smaller list based on metrics, you then deep dive and make your final selection.
This also holds true for keyword difficulty scores, website traffic, or any other type of bulk data analysis.