The portrayal of an ex-Stormtrooper: The Finn poll

Then there's no point in an ST at all and especially no need for new characters. The OT characters would've been able to stop the First Order on their own and not need anyone.

Like I said, the OT characters would've dealt with everything and not need any help.

The Mythos and Lore ended with ROTJ, the only way new characters would fit into that and be leads in their own right would be to make them incompetent useless sidekicks that the OT characters wouldn't need.

Because the OT characters couldn't deal with the First Order on their own and new characters were there to take over. And these new characters weren't introduced as useless sidekicks but independent characters in their own right.