I know that katalon technology is built on top of selenium.
I also know that Groovy have some very powerful features for testing.
But still, is katalon a little bit underestimated?
In which way should someone choose with one of the both to use after all?
One of the differences between Katalon and groovy is that groovy is lightweight as compared to Katalon. Since Katalon offers variety of features in a container, it is easier to use. Scripting is very much encapsulated within it. Groovy on other had provides many features for testing - Do check out Spock (http://spockframework.org) which is mainly used for testing Java/Groovy applications.
In a nut shell; which should be chosen really depends on the team composition of programmers, tech stack on which your app is built, maintainability of the application in scope. Hope it helps...