The advantage of a ramjet is it uses the oxygen in the air instead of its own oxidizer, so its actually lighter for the same sized normal missile since it is not carrying an oversized sustainer with an oxidizer component. The usual missile would have gone 25-30 km with a typical accelerate, coast, decelerate profile as versus the Akash's accelerate-sustain profile.From what you are saying, I gather that the 25 to 30 km range will be where the missile will be really effective. So we could have used a different propulsion system, making the missile even lighter with the same energy thourghout it's light path.
The other way to get similar performance is to use a dual thrust motor, with the second section kicking in for the end game engagement.
There are pros and cons to each system.
In the case of the Akash, the use of a ramjet allows for a sustained high energy missile. With a dual thrust motor, it becomes far more complex, as the missile accelerates, decelerates and then again accelerates, decelerates. Basically, remember, guidance algorithms have to cope. The guidance radar which is controlling the missile from the ground has to be constantly monitoring the missiles energy state. All this will add more complexity to the missile, which means cost, and which also means more chances of delay & even lower performance till everything gets worked out.
The ramjet method is more robust, with its only disadvantage being that a constantly high speed does not allow the missile to "slow down" to prevent overshoots. However, that is sort of a moot point with the Akash, because if it passes within 50m of the target, it will detonate, taking out the target.
Overall though, the question of weight has to be seen in context with regards to the user requirements. For the AF, the Akash replaces the SA-3 Goa , which is much larger (953KG in weight as versus 720 kg for Akash) & in fact, less mobile, because its radar units and other ground systems are static. For the Army, the Akash will replace the SA-6 regiments, and is in all likelihood, more mobile as it is now fielded on T-72 tanks (this new requirement fielded in 2002 by the Army, and developed by the DRDO by 2007).
A typical Akash battery has 4 launchers, each with 3 missiles. Thats 12 missiles at any time, ready to fire. Assuming two per target, an Akash battery can engage 6 targets, which is actually two more than the maximum a Battery Level radar can handle. So taking 3 per target, thats actually 4 per radar, which is exactly what the Rajendra can handle.
Point is the entire system is fairly well thought out & able to handle a flight package of 4 fighters, the exact sort which the IA/IAF know is usually the case. Given multiple batteries of Akash will be usually deployed to protect a vital place, the number of targets it can handle scale up & the weight per se, is not a deal breaker. An Akash squadron AF (2 batteries) can handle 8 targets at any one time, and the Akash regiment/group for the Army, can handle 16 targets (4 batteries). Given an entire squadron is usually 16 fighters (with 2 attrition reserves), its pretty much overkill.
The limitation in the above is the number of FLR/BLR, deploy more of these and the number of targets engaged, goes up.
The overall point is that the Akash, with its ramjet missile remains very potent.
A lighter missile with a more complex layout is possible (that is what the Barak-8/LRSAM is) but it will also be more expensive & come with its own issues. Cost effectiveness is a pretty important criteria.The Akash can very usefully serve the role of a relatively inexpensive missile, with a huge inventory, able to handle even complex targets with heavy ECM