jboss-web_15_0.xsd of WildFly 27.0 is not included in the xml catalog. It has a different namespace:

        <jboss-web xmlns="urn:jboss:jakartaee:1.0"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           xsi:schemaLocation="urn:jboss:jakartaee:1.0 https://www.jboss.org/schema/jbossas/jboss-web_15_0.xsd"
           version="15.0">

Same for "jboss-client_9_0.xsd" and probably several others. Could you check the full list of xsd files?

This cache gets more relevant, as recent Eclipse releases have disabled download of external XSDs by default, which results in a warning: