As for "no player left behind", it is good in theory but in practice is a difficult problem of encounter design because without things like time pressure or multiple simultaneous problems or splitting the party or what not, there is no pressing reason why an unskilled party member needs to do anything and a strong reason why the rest of the party might want the Barbarian with no social skills to keep their mouth shut. It's not really something system alone can solve, as optimized play may well involve letting one player character do all the work while the rest watch and it's very hard to have verisimilitude and not have that occur. So as a GM you have to be trying to create complications that will force the party to have to work together on the problems they face. That's for various reasons I've discussed before easiest in combat situations, but you can if you work on it come up with strategies for encouraging everyone to participate. Albeit, some of those strategies like splitting the party will lead to you waiting 30 minutes for your turn, so there is still a need to cultivate both the enjoyment of watching other people play and the skill of being an entertainer to your fellow players so that your play is fun to watch.