His idea is not bad. A 50km+ anti-ship torpedo brought to the target by some low-flying missile would complicate the defence of a ship.
A torpedo is a substantial item and a long range torpedo even more so... which means what we are actually talking about is a small light short range torpedo... which are generally most effective against submarines.
A torpedo big enough to have a decent range and payload punch to sink a decent sized ship would be very long, very big, and very heavy and would not balance well on the end of a rocket.
Lets just say that such a long range torpedo would be about 53cm wide and about 8 metres long so to deliver that by air to a target you will need to bolt a fairly enormous solid fuelled rocket engine on the back... a jet powered weapon would need a huge solid rocket booster anyway and a huge wing just to fly.
Most ships could probably defend themselves from ballistically launched mach 2-2.5 missiles better than they could defend against a torpedo that spends its entire time in the water.
The point is that the few weapons that consist of ballistically fired small torpedoes are for use against subs with no air defence systems or radar so really they don't hear anything coming... the weapon just splashes into the water a few kms from their position and then the detect the running scanning torpedo when it is in its final attack mode.
That makes sense because flying at mach 2 for 40kms means it covers the space to the detected sub quickly and for the target sub silently.
For use against a ship however it is an obvious and fairly straight forward target during its ballistic flight and to get within 3-5km of the ship puts it well within range of most medium range SAM systems.
The multi stage system only really makes sense in specific cases and it really depends on the targets involved to make it worth while.
Ie sub means no air defences and small torpedo which means not so huge overall weapon size.
For the supersonic Club, the subsonic cruise missile portion gives excellent flight range at a low speed but at a low radar evading altitude... but when actually attacking the target the rocket section accelerates the terminal portion of the missile to mach 3 which gives it the benefits of long range and relative low cost, but with the benefits of good defence penetration performance and terminal effect.
So you end up with a long range weapon with a good chance of penetrating even modern air defences...
The combination is balanced and uses the best features to achieved desired characteristics...
The first stage is a slow burning cruise missile tubofan, and the last stage is a rocket powered torpedo with a super-cavitating nose. Similarly I would like to see a torpedo (or a UUV drone) that get close enough to a boat (100-50km) and launches a rocket powered Ashm out of the water at Mach 3+ speed.
But why bother with the turbofan portion... what about a low noise torpedo that runs at perhaps 20 knots for hours on end that can deliver a nose full of 10-20 rocket propelled torpedo final stage warheads that are independently targeting enemy ships.
An enemy carrier group is making its way across the Pacific or Atlantic... it wont be sailing straight but a huge torpedo with 10-20 rocket powered super cavitating torpedoes in its nose could be launched in the general direction at perhaps 20-30 knots on a roughly intercept course... as it gets close it can move to near the surface and receive satellite information and course corrections to intercept the surface action group... eventually the weapon will get to within a few kms of the enemy ship grouping and it could launch its rocket powered high speed torpedoes at the ships from very close range... perhaps even closing head on with the enemy ships the main torpedo carrier operating at very low speeds now could turn 180 degrees and wait for the enemy ships to sail past and launch an attack from behind... wake homing torpedos or just passive sonar torpedoes chasing the propellers running right in front of them... the carrying main torpedo could simply sink now that it has done its job without risking a much more expensive manned sub... or it could ram one of those propellers in front of it too with its own modest HE payload.
Both could be developed/enlarged to carry a Kh-35.
But would you not agree a torpedo would be more difficult to deal with than a subsonic anti ship missile?