All of these basic builds say they don’t fare well in large-scale group content… what as a new player can I work on to be able to do large-scale stuff?
These basic builds are mainly aimed at good PvE clearing and sustain. Group content is more focused around individual roles where you have tanks for CC, healers for sustain, supports for utility and damage dealers completely focused on doing area damage to enemies.
In my opinion the best thing you can do to prepare is to join a guild and check their guild loadouts. Most guilds usually have a variety of loadouts for different roles that they will ask you to wear and fame up. If you know what role you wanna play some people could probably help you out and suggest some builds for it.