This has no impact, because we have no reason to think the planets with oval orbits are smaller than whatever other planets they may have had close encounters with.

This weakens the argument by suggesting that planetary orbits being affected by other planets might not be as likely as comets being thrown into oval orbits by planets.

This strengthens by helping to establish one of the assumptions: some distant stars have multiple planets orbiting them, which is required in order for the author’s theory about close encounters between planets orbiting the same star to work.

We already know that many comets orbiting our sun have been thrown into an oval orbit by other planets. We don’t need additional help establishing that comet orbits can be affected by planets. We need to show that this effect can happen to planetary orbits.

This weakens the argument by undermining the plausibility of the theory that planets with oval orbits were thrown into those orbits by other planets orbiting the same star.