Good analysis! A few remarks:

In practice even for a planet with as thin an atmosphere as Earth, getting past the atmosphere is more difficult than actually reaching escape velocity. One of the most common times for a rocket to break up is near Max Q which is where maximum aerodynamic stress occurs. This is generally in the range of about 10 km to 20 km up.

In worlds too big to escape by propulsion, people may come up with the idea of the space elevator, but the extra gravity will require taking into account the structure's weight.

Getting enough mass up there to build a space elevator is itself a very tough problem.

Some world out there may have a ridiculously tall mountain that extends into the upper atmosphere. Gravity at the top will be lower, and if a launch platform can be built there, takeoff will be easier. Of course, this is an "if" bigger than said mountain.

Whether gravity is stronger or weaker on top of a mountain is surprisingly complicated and depends a lot on the individual planet's makeup. However, at least on Earth-like planets it is weaker. See here. Note though that if a planet is really massive it is less likely to have large mountains. You can more easily get large mountains when a planet is small. (e.g. Olympus Mons on Mars).

India has a huge coastline, but for mythical/cultural reasons, Hinduism used to have a taboo against sea travel. In the worst scenario, our heavy aliens may stay on ground, not because they can't, but because they won't; maybe their atmosphere looks too scary or their planet attracts too many meteorites or it has several ominous-looking moons or something.

This would require everyone on the planet to take this same attitude. This seems unlikely to be common.