Vendor metrics - subsystem - statistics-enabled to get valid data
I was playing with vendor metrics and I received a lot of zeros.

curl http://localhost:10090/metrics/vendor 2>/dev/null | grep -v TYPE | grep -v HELP | sort

Note: I use -Djboss.socket.binding.port-offset=100

So I started to wonder why and it's because of statistics are not enabled.
When I enabled statistics for Undertow and hit the WF server main page I saw some changes in metrics.

subsystem=undertow/:write-attribute(name=statistics-enabled, value=true)

Later I realized this scenario is also mentioned in analysis, section WildFly Metrics with undefined value / statistic-enabled = false
https://github.com/wildfly/wildfly-proposals/blob/cc189b56720951875aa96102f876ac0399930f9c/microprofile/WFLY-10712_microprofile_metrics.asciidoc#wildfly-metrics-with-undefined-value--statistic-enabled--false

So this is mainly tracking + discussion point now.