Vivek, as usual your post is detail oriented and Singha has captured the theme correctly as 'flying artillery', here is a simple minded response,
a) Line of Sight: You are talking about helicopters. Slow and unwieldy compared to aircraft, correct? So their survivability in the face of enemy depends on being able to take advantage of low altitudes above ground level and terrain masking. If you are low and close the ground, generally speaking the terrain will not allow LOS beyond certain limits unlike high altitude aircraft dropping PGMs or low altitude aircraft flying higher than helicopters but having the speed and ruggedness to survive hits from enemy fire. Plus they (the aircraft) have the altitude to deploy IR countermeasures and ECM more effectively. The helicopters need weapons that fall within the ~10 km range for most targets they are ever likely to see. Anything beyond that you bring in fixed wing aircraft.
The LOS limitation may not continue to apply in the age of network centric warfare where the sensor is separated from the shooter, the Mi-17 will just play the role of the shooter. In that case 10km needn't be the threshold, these days there is also a plan to equip GMTI/SAR radars on choppers and the UAV's are already there
b) Energy: Why are these munitions so small and light? Consider the kind of weapons that a helicopter deploys. It is not dropping free-fall bombs overhead, is it? Its not dropping stabilized munitions from high altitude like aircraft do. So it can't depend on converting potential energy to directed kinetic energy during free-fall. So what its needs is munitions that go more horizontal than vertical when they are fired. It needs munitions that can fly or it needs munitions with very high momentum in the horizontal than the vertical (rockets fired horizontally experiencing ballistic drop). When you consider that, you notice that helicopter-fired missiles and rockets therefore require the same argument as to why aircraft need to be as light as possible: the Thrust-to-Weight ratio. Missiles have to have as high an impulse assigned to them in the horizontal direction and as quickly as possible. Hence the horizontal tube launched stuff: rockets and TOW missiles (and all other anti-tank missiles in general). Now, if we are talking impulse, could we simply not scale it up? Make the warhead bigger by adding a bigger rocket motor behind it, thereby maintaining the TW ratio? Yes you can, and some Mi-24/35 rockets (S-24?) do in fact use this concept when LOS allows. In most cases, where you can increase the size of the warhead, the LOS issue in point (a) above becomes dominant.
Yes passive propulsion munitions would need enough altitude for say the Sudarshan kit to do its magic of precision and still achieve the requisite stand off range, so they are ruled out on the Mi-17s. Maybe high altitude capable Choppers like the Rudra or the LCH can consider them. Its my tunnel vision for AAC that makes me forget about IAF
d) Accuracy of munitions: rockets and other unguided projectile munitions (30 mm cannon rounds included) have a tendency to splatter all over the place. Hence the optimization for larger numbers of lighter (yes) and shorter range (also yes) warheads to allow target saturation. If we changed an Mi-17 loadout from S-5 rockets to S-24 rockets, you can carry one per pylon of the latter compared with half dozen or more (generally more, lot more) of the former. Which is better? It becomes a question of target spread and kill over-pressure required. Usually for the kind of targets engaged with unguided rockets, the wider spread of larger rocket numbers is usually sufficient. S-24 type warheads are better left to fixed-wing aircraft to deploy against hardened targets. If you do encounter a semi-hardened target like a bunker or something, an anti-tank guided missile will be better and usually sufficient.
Yes while having multiple smaller rockets than one large inaccurate rocket on the pylons makes sense, the Mi-17 is a transport so it can carry reloads in the cabin. For NLOS targets one needs large rockets and its their accuracy issue that needs to be addressed like using GPS antenna patches etc. Except in mountainous terrain, altitude is not really needed for firing precision rockets which means we can avoid the case c) high altitude and heavy pylon load, however higher altitude is preferred
In one of the episodes of your mil scenario thread, there is a situation where the Pinaka reload vehicles are stuck on some muddy path while the launchers themselves are positioned to fire and they are very much vulnerable having given away their position in their first salvo, it brings out the point that the logistics tail could be a liability in a ground based system.
Consider the scenario, the Mi-17 takes off from a base with few rockets on the pylons and reloads inside the cabin, reaches a airspace sector based on the mission, fires the first salvo against the provided NLOS-target info, travels to a nearby makeshift helipad, a reload is done (assuming a vehicle is pre-positioned for such purpose, even a reload vehicle in such case, there is no way to avoid this unless the Mi-17 system is made as a self-contained one) and again reaches the sector fires the next salvo and then reaches back to the base. The airspace sector of the launch area is no where near the frontline to threaten its safety, and due to its mobility the enemy artillery locating radars cannot pinpoint its position to direct counter fire. The exact bang-for-buck matrix of lethality vs. numbers of the rockets can be worked out based on the mission
and the frontal reach is quite large with an airborne system.