I agree. A ship class based on the role is much easier to figure out, and much more decriptive at a glance. If I see \"fighter\", I\'m not doing equations in my head to figure out the mass to thrust ratio; I\'m thinking, \"Oh, it\'s a smallish ship that zips around and shoots things.\" Knowing size is important, though, so I would suggest a two-part naming convention: The first part based on mass (Light, Heavy, Titan...), and the second part based on role (Fighter, Bomber, Carrier...). Then if you see \"Titan Carrier\", you know how it\'s different from \"Titan Destroyer.\"
The only real speedbump is figuring out the exact names so that it doesn\'t feel like things are overlapping. For instance, \"scout\" sounds like it could be the size OR the role of the ship.
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In regards to the main graph you\'ve given, though, I can barely make heads or tails of it. The sections are shaped so odd and go all over the place. \"Bomber\" seems to include a medium ship with turrets, or a larger ship without turrets, but not a larger ship with turrets. It\'s very confusing. If you\'re going to go with that sort of naming convention, you need to make boundaries very clear.