That's half correct. Marle's pendant just happens to react with the teleporter initially. The pendant is no longer needed after Lucca makes the gate key.

I think the point of CT is that nobody is in charge really. Nobody makes leadership decisions. Heck Crono doesn't even speak and canonically dies. But if one thing is certain, it is that Lucca is the brains of the entire operation. She is responsible for making the teleporter, gate key, understanding time travel and paradoxes to plan, repairing robo, invented the first robot in general, broke Crono out of jail, helped Crono save Marle from paradox/death, etc. All of these were essential to progressing. She's even a huge part of Chrono Cross. Without Lucca, none of this is possible.

It's silly to negate all of what Lucca did, just because Marle happened to stumble with some jewelry on into a teleporter and was Crono's gf. Other than that, she was an accessory. If she didn't have her pendant, she wouldn't even be really relevant to the story and she could have died in 600AD and it wouldn't have mattered. Can't say the same about Lucca.