For a measure that will help curb the tournament lists, this is what I'd consider: make a list of all the pilots in the highest-performing meta squads, and allow people to only bring one pilot from that list in their squads.
Nothing is banned; players can still fly any individual ship/pilot they want to. Some players will still try to optimize lists within the limitations, because that's how some people play, but at least you'll be fostering some innovation.
Also maybe be a little bit more clear about what constitutes a 'beginner', and tell people that if they're a bit more experienced they're still welcome but if they do come please please please bring a silly/thematic list, or else maybe open a side table so they can play games and give pointers to the less experienced players. Or even just run a split tournament with a beginner's bracket and a tryhard bracket, if that's the kind of thing you can pull off.
