The default instrumentation that comes with node_exporter covers far more than what systat provides. Retrieving data from /proc at every scrape also gives you a more accurate timestamp, which helps reduce graph artifacts.
As an aside, if you have machine-level cronjobs you want to expose metrics from you can use the textfile[1] module of the node_exporter, which reads in data from *.prom files in the same format as accepted by the Pushgateway.
