Well the point of having energy-weapons be anti-robot is mostly gameplay-related. So you should collect different weapons for different situations.
As understood from my first post, the game is not at all suitable for details such as having target movement effect penetration (that might be realistic though im not very familiar with science-fiction weapons). Neither will there be different damage classes for different energy weapons.
Yeah robots work sort of like armoured but with a twist (mainly regards to energy, fire and explosives). Fire = anti-organic, Explosion = anti-robot.
But some game do use energy-weapons as anti-robot, so i hope the concept doesnt seem TOO unintuitive?
And what about the other stuff? The numbers and how i divide melee weapons between normal and piercing?
Okay, in this case its kinda "anything goes"... you can always come up with "explanations" if something is not really how stuff works in real life.
I see Thaumaturges point, if we are talking about CHEAP entertainment class electronics devices, true, not much stuff will be redundant (which is why many of the cheap electronic devices like USB Stick will certainly die within years, while you could theoretically build one that will keep going for decades)...
Depending on what the backstory is behind your robots, that might actually make (some) sense... entertainment robots built for home use for example instead of military robots (which should be tough as nails, the difference should be even greater than between average john doe and an elite soldier).
Well, yeah, most games treat the term "energy weapon" as another word for "weair magical device we cannot explain ouselves", and then find sciency sounding names to make people believe this is still "science fiction" when it has basically become "fantasy in space" long ago.
About 5% of Star Wars is Science Fiction... the Rest is all fantasy.... those lasers and light sabers and even their space craft physics? All made up for maximum cinematic impact, not based in science at all. "Lasers" where just all the rage and really science-fiction in the seventies, that is why george lucas called his weird beam weapons lasers.
Star Wars and George Lucas never did take the time to try to come up with explanations, they clearly didn't have sciencists and technicians as consultants when they created the first 3 movies, and they didn't care about it in the meantime.
Now, I am NOT a particular fan of mixing fact with fiction WITHOUT giving audiences a particular hint about which is fact and which is fiction... which is why I DO like mixing science-fiction and magic (never been troubled by the force at all), but I highly dislike when something called like something from the real world doesn't work like it does in the real world (in case of Star Wars "Lasers", light moving way slower than lightspeed, a laserbeam being visible even without dust particles in the air, or making a sound when the beam zips by).
But that is me and my Nerd rage. I personally would call a weapon that is basically "future tech so advanced I don't understand it myself" by a name that isn't recognizable to other "raging nerds" like me that might pick your game apart because your laser do not follow normal laws of physics. Calling it a "death ray" or "particle beam" allows you to come up with your own "physics" that do satisfy the needs of your game design without having players bicker about you bending the laws of physic. It is, after all, incredibly advanced future tech... which is indistinguable from magic... and we all know that magic is used as a "deus ex machina" very often to explain stuff in games that just has to work the way it does for gameplay reasons.
Apart from that naming issue, your energy weapons can basically do whatever you want them to do. As soon as you abandon realworld examples (which there are not many really built ones anyway of besides lasers and maybe some microwave based weapons), your imagination is the only limitation.
About your close combat attack types, sound about right to me... piercing doing more damage to organic creatures could model how they have a bigger tendency to suffer from bloodloss.
I am still not 100% onboard about mechanical creatures taking more damage from explosions... but again, you could come up with some explanations....
e.g: The robots are old rust-buckets that haven't been properly maintained for years, and cannot maintain themselves. They will keep going until their nuclear core malfunctions or their frame collapses under its own weight after taking enough damage from rust and the weather, but they have become more fragile than some of the mutants running around.
While they still don't bleed when cut and don't care much about heat, their shells and frames have become quite fragile and will collapse quickly when blown up with explosives.
If you frame the backstory correctly, almost anything is explainable somehow. You CAN imitate star wars in not even trying to explain things, if you are ready to face some nerd rage and people calling you out on it (George Lucas reply was simply "The Star Wars Universe follows different laws of physics" )