Do not underestimate the power of the time travelers.
In 65 million BC, Lavos impacted the surface of the earth at meteoric speed, creating a fireball that covered most of the continent and caused a global climactic change that lasted for millions of years. This explosion is similar to the K-T Meteor impact, which is estimated to have released energy equivalent to 100 trillion Tons of TNT.
The K-T impact vaporized, melted, or ejected over 200 thousand cubic kilometers of the earth's crust, producing a crater 180 kilometer wide and several kilometers deep. The object penetrated 15 kilometers into the earth before being almost completely vaporized.
For comparison, the most powerful hydrogen bomb ever produced had a yield of 50 million Tons of TNT, and the total world nuclear arsenal has a combined yield of approximately 5 billion Tons of TNT. The explosion of Krakatoa, the most violent volcanic eruption in recorded history, released energy equivalent to 200 million Tons of TNT.
These are the facts1.) Lavos withstood an impact equivalent to 100 trillion Tons of TNT without harm, but Crono was able to hurt it with his sword and magic.
2.)Lavos ruined the surface of the earth in seconds (releasing even more energy than its impact), but Crono could survive its most powerful attacks in a fight to the death.
In order to defeat Lavos, the travelers must have incredible abilities. Although mortal, the travelers faced Lavos as an equal in power. The blows exchanged in the final battle with Lavos were earth-shattering. No weapon available to Porre could begin to compare.
No matter how powerful and effective the travelers' weapons and armour were, they had to endure some fraction of these energies, which still makes them super-human. Given these facts, it is entirely reasonable that Crono, unclothed, could survive the simultaneous detonation of every nuclear weapon on earth piled around him, let alone a bullet.
To think that Crono would be concerned with any number of common soldiers or mundane weapons is absurd. If Crono participated in a war with Porre, entire armies would annihilated by his attacks. Only the most elite warriors with high level elements, like Norris or Grobyc, could offer even token opposition, and they would be inevitably defeated.
The time travelers did not participate in the fall of Guardia or the events of Chrono Cross for unknown reasons, not because of Porre, simply because they are too powerful.
