I am writing lore for a project and am mostly clueless about gravity's effect on human beings in these circumstances. The brief history is that bronze/iron age people had access to "primitive" technology enabling them to sail from one planet to another, enabling thousands of fighters transitioning from spears to early gunpowder. This was through usage of a gravitational phenomenon that lasted for several thousand years precisely for the two Terran planets as if their atmospheres were in synchronization.
The 0.8g planet is an arid planet with oceans and signature flat savanna's with some tropical regions naturally about. This planet frequently sent aggressive war parties to the other in recent history before the advent of industrial warfare and melee was mainstay, being historically more centralized.
The 1.4g planet was originally going to be a sea-less world with high elevations. Now, to broaden its depth, it consists of small seas and great lakes, with "continents" being entire valleys, grand canyons, massive Nile-esque rivers, and endless hilly Virginian terrain, often isolating tribal states and civilizations like China and Britannia was.
Most people on both planets have completely acclimatized to their native gravity, perhaps even genetically, to the point births on the 1.4g world are 2/3rd's lesser but their people are shorter and much more stronger and reflexive, whereas the 0.8g human's are naturally taller and weaker.
The third planet to appear is a barely colonized 1g planet basically like Earth's conditions.
So how would humans, typically military-trained handle landing and warring on the opposite planets? Overtime I would assume they would train and be prepared for the radical differences, but I assume fighters from the 1.4g world would more often than not crush the lighter-humans, as warfare transitioned from melee weapons to industrial weapons, correct?