@bajax @snacks The idea is that the combustion bots are early military models and industrial models, the basic spacetech ones are military tech available to all nations, and advanced ones are top of the line built only by the great powers or powerful private companies.
Fantasy energy source material is somewhat limited, basic ones use dust that is easier to get, advanced ones use little shards of it. Special endgame boss robot uses a huge piece of it. Militias, outlaws, and backwaters still use the diesel ones because they can be manufactured and mantained without any special tech using normal factories so they're very cheap, and can still mount big cannons or missiles despite being much slower and incapable of using energy based defenses.
Scrapping enemy bots or getting pieces or tech blueprints through alliances or espionage and having engineers work on those to build/reverse engineer will be a big part of the advancement mechanics, otherwise players are limited to what they can capture or buy/be given in contracts or negotiations.