Graviton beams are the only kinetic damage energy weapon. As per their description, they are supposed to be specifically for damaging shields, which they are horrible at, because they're beam weapons and because their damage is tiny.
Pulse lasers are indeed better at damaging shields. They generate obscene amounts of flux on your own ship, though, and the damage per shot is not very good, and ends up just being average. It is a ridiculous waste to use antimatter blasters against shields in particular unless it is a very special situation, as they generate 1500 flux on you every time you fire one, for a mere 1000 damage on enemy shields (minus shield efficiency, so much, much less on 0.8 and lower shield absorption ratios). There's a very good reason AM blasters are classified as strike weapons. Clever maneuvering on a player controlled ship can mitigate these drawbacks, however, and make it possible to take advantage of unique openings that AI would miss, but that's only relevant in small-scale, small-fleet, beginner campaign situations. We're talking about balance for the entire game here, and taking large fleets into consideration.
You also seem to have misread what I typed, as I was talking about sabots as options FOR high tech ships, not AGAINST them. With that in mind, you raise another point that strengthens my own, that they are very slow and easy to dodge and destroy.
As for your experience with pure-energy-loadout medusa, it should be easy enough, I imagine, to outlast an Onslaught's ammo supply, and/or circle around to its unshielded rear and do quick strike runs until it's dead while avoiding its attacks. That's the advantage of player-controlled ships. Of course, that was not at all my point, and furthermore is an idea that quickly falls apart when you get past the beginning campaign stages and actually have your team AI battling enemy AI.
Firstly, it does not follow that simply being fast means that a ship can punish anything that can catch it. If you meant maneuverability, that can be true for player controlled ships, which is but one small facet of the game's entirety considering potential fleet sizes, but even then a given ship can all too easily be extremely outclassed when its focus is shields at the expense of armor and hull when the enemy has plenty of kinetic damage to pour on, especially since explosive damage is commonly accompanying it in ballistics.
Secondly, there is absolutely no shortage of high range ballistics, especially kinetic damage based ones. Off the top of my head, there are railguns, needlers, hypervelocity drivers, autocannons, which range from 600 to, what, 1000 range? They are often extremely fast projectiles, have tons of ammunition, and deal way, way more damage to shields than the flux they generate on the user from firing them. And that's just in the small ballistics category. Energy weapons do not compare in range, and the ones that compare in accuracy are beams, which are useless against shields.
Again, you're only considering early game, tiny fleet sizes, and the single player-controlled ship in small scale battles. Also, there is no "ballistic medusa" in the base game, you're thinking of a mod. If it was just a reference for the sake of comparison, I would mention the ballistic version of the hyperion frigate from the same mod, which is vastly superior to its energy counterpart. Try it. 2 dual MGs in front 2 mounts, 1 annihilator pod on each of the 2 med missile mounts. Extend missile ammo for more lackadaisical barrages, and enjoy dispatching ships two size categories larger with ease because you can break their shields in seconds. Works against entire fleets, even ones containing the weaker capital ships. Just one ballistic frigate.
The medusa looks good on paper, and its maneuverability alone lends it unarguable advantages when in the hands of the player, but in practice and in actual fleet battles of even moderate size, they fall apart to the superior combination of kinetic and explosive ballistic weapons, nevermind missiles flying around that PD beams cannot even begin to handle.
All of you guys should really try pitting decent sized or higher, equal fleets of high tech ships with equal crew level against low tech fleets. The advantage of kinetic damage is obvious, and nobody survives long enough for ammo to run out except on missiles (which high tech ships often rely on to make up for their lack of armor or shield damaging capabilities).