The Moscow ABM system is not efficient. It is based on the intercept of RV in the terminal phase using a nuclear warhead. The US had such a system 50 years ago and dismantled it.
Using a nuclear warhead to assure a kill is very very efficient and also deals with any problems like a target with a jammer or decoys that might distract a hit to kill interceptor that either hits or fails... or even might detect the incoming interceptor and fire some side thruster rockets to jump sideways by say 10m in the split second before impact... with the closing speeds of these objects there is no time for the interceptor to make the same move so it would be a guaranteed miss every time... and before you cry about no weapon doing that... the TOR family of missiles have side thruster rockets around their nose used during launch to point the missile in the direction of the target at launch, but are also used in the terminal portion of the engagment to manouver the missile to get a more precise hit with a hard manouvering target... but it is not hit to kill either because fragmentation warheads are vastly more effective across a much wider range of target types than a solid warhead.
The US system was dismantled because they built it around an ICBM field and even an idiot could have told them that an ABM system around an ICBM field is a waste of time because by the time any Soviet ICBM warheads or SLBM warheads arrive to destroy the ICBM field the ICBMs would already have been launched and would be on their way to their targets... destroying empty silos is a waste of warheads.... the Soviets didn't even aim any missiles at US silos... they aimed them all at US population centres...
Now it is being expanded to A-225. Nothing is known about him, but he still intercept RV with the 53T6M in terminal phase. It is not known whether it has a conventional or a nuclear warhead.
So you admit they have been testing and upgrading the system since it first entered service... that is good... the fact that it is not known as to whether it is a nuke or a hit to kill is irrelevant. Hit to kill would be nice but unnecessary and much more expensive and complicated... destroying incoming threats with nukes is easier than trying to hit them directly. With nuclear warheads to precision requirement to stop a threat is dramatically reduced and made simpler... the cost is that there will be a lot of nuclear explosions above the target being protected, but that is much better than nuclear explosions in the target being protected...
Russia still has no HtK technology in either the S-400 or S-300V4 systems.
What successful HtK technology are they currently operating in service... PAC-2 has poor performance against ballistic targets and PAC-3s record is pretty sketchy too...
This is a technology lagging behind the US.
They are probably lagging behind the US in teeth whitening chemicals too but I really don't think that is important either...
Their current SAMs are pathetic to ordinary... even their allies don't want Patriot or THAAD and would rather disrupt their economic relationship with the US and buy S-400s even if it means missing out on F-35s... and after their tests they said the S-400 is even better than they were promised...
Maybe it won't be until the S-500 that the RV interceptor l will be used with the HtK warhead!
I doubt they would bother with HtK warheads... they are simply not flexible enough to engage the wide variety of targets the missile is intended to be used against.
Most likely they will continue to use their smart fragmentation warhead that senses the location of the target just before impact and explodes directing a targeted shower of fragments at the targets expected position... the difference between that an a hit to kill warhead is like the difference between a shotgun blast and a rifle bullet being fired at a small fast moving target. The shotgun blast is vastly more effective in terms of hit probability... when used correctly it makes hit probability 100%. With a rifle bullet hit probability is never 100% and often even with a hit it is not enough to ensure the target is destroyed as it might not hit a critical point of the target. A blast of fragments directed at a target means multiple hits and assured kills... against a variety of targets from small warheads through cruise missiles as well as aircraft and drones and even ground targets.
There is no evidence that the S-400 is more effective than THAAD and PAC 3. Maybe against air targets, while US systems better combat ballistic missiles.
There is abundant evidence that S-400 is part of the Syrian air defence network and since the Syrian air defence components were added there have been no surprise attacks... THAAD and PAC-3 are poor systems in comparison and are much much more expensive and really only cover ABM threats up to Scud levels of performance.... mach 7... which means even Iskander is too fast for them even without manouvering. S-400 can deal with targets moving at almost 5km per second... which is about mach 17 - 18... and it can deal with aircraft and drones and missiles and cruise missiles etc etc...
The US systems exceed the Russian and Soviet systems only in price. Saudi Arabia is covered in Patriot systems yet subsonic cruise missiles and drones penetrated their defended airspace without even being spotted... pathetic.
Note the Igla MANPAD had impact and graze fuses only so for very small targets like a drone or an anti tank missile like the AT-3 if it didn't hit the target directly it didn't intercept it... During testing out of 9 targets the Igla destroyed 5, but in four cases did not actually make contact with the target and therefore the warhead didn't explode and the missile just flew past the target by your logic with your HtK bullshit what they needed to do was fit the MANPAD with a 50 million dollar AESA radar controller to more precisely track the target and the outgoing missile and then spend another 10 million dollars per missile with a digital data link to allow more precise course corrections to ensure a direct hit... what the Russians did was spend a few thousand dollars and upgrade the missile with a proximity fuse and created the Igla-S.
Americans are experts at spending money and their resulting systems look really good to fanboys... Javelin is a case in point... on paper amazing... in the field not so great and too expensive to use in large numbers. The Metis ATGM has similar range and better penetration and you can literally buy 100 Metis missiles for the price of one Javelin missiles. In terms of combat use the Metis is superior and can be used in large numbers against all sorts of targets... Javelin will be used against all sorts of crap too but we don't have any more because they are too expensive...