"Do you want to be the first one to start?" Evelyn asked. "It looks like you have worked hard in the past few weeks. Not only do you now have a high amount of ena, but the ena around you seems to be more stabilized."
It appeared Evelyn was asking him to check his current power. In the end, increasing one's ena tremendously wouldn't be too beneficial.
While the nobles could feed their sons or daughters with a bunch of cores, they wouldn't have the technique to utilize them.
In other words, the ena would be useless inside of them. In exchange, consuming a large number of cores will take time as well.
Nathan only got a few tens of cores, but it already took him close to three days to absorb everything. What if he got a hundred mature class cores instead? It might take close to a week.