This argument is based on the idea that Reliant went to Ceti Alpha to find a planet in an exact spot. It didn't. It went to Ceti Alpha to find a specific planet, within tolerances, which it did. Was that planet in the exact orbit the computer said it would be? No, but that can be explained by orbital drift over the years since the last scan was made. Anything, and I mean ANYTHING, can change the orbit of a planet. It may get hit by an asteroid. A nearby pulsar may have intermittent gravitational effects. Is scanning for these things part of Reliant's mission? No. So they don't do them. They just find the type of planet they're looking for, and go there, even if the orbit is off.
They don't navigate? I don't find that at all believable. If they are going to a specific planet, that is a question of navigation. Starfleet has a strong navigation emphasis, using starships for mapping duty, keeping extensive charts, a navigator at the controls at all times etc. If that planet is not where the tables said it will be, that's a pretty big red flag for a competent navigator to overlook. If it is so common for orbits to shift, etc, that would argue for more diligence and verification by the navigator, not less.