You know, we don't even know if in the original timeline, Porre took over. There being an Arris dome run by the descendants of Marle doesn't really prove anything.
Also, Crono and co are mortals. There are reasons why they could defeat Lavos, most obviously because the entity chose them or whatever, and as Gasapr said, they were empowered from their experiences. In theory, if someone like Tata joined them, then he could kill Lavos too. Now you're thinking "WTF". Obviously there is a reason why they won. I doubt Crono could withstand a gunshot wound. His skin isn't steel, and if they truely were invincible, Lucca would not have been kidnapped, surprised nor resisted. If her power was that great, she'd have killed them inside Chronopolis or at her house.