They can't stop drones, they can't stop glide bombs and they cant stop cruise missiles.
To be fair if they could not stop any of those things we would not be talking about three destroyed we would be talking about having none left and needing more to be sent to replace them.
Regarding costs I wonder if they are considering that new BMP-3 system with the 57mm gun turret... it has no radar but fairly extensive night and all weather optics and air burst shells should allow it to rather efficiently lob a few shells into the path of incoming threats to destroy them.
Mention of the air burst 30mm shells seemed to suggest they used a rear facing laser sensor so the rounds are monitored as travel towards the target and when they get a specific distance from the target a laser beam is directed at the shells and they explode.
It sounds really complicated, but the alternative is an incredibly precise timer... that is micro second accurate so the trajectory of the target and flight time of the out going round can be used to calculate an intercept point in space... that shell distance minus say 5 metres and then the shell is fired and 5 metres before impact the shell explodes spraying forward a swath of fragments like a claymore mine.
The problem is that such levels of accuracy needed make those timers rather expensive and obviously being located inside the shell are destroyed with use.
This new laser method means all the expensive complicated calculation and timing components can be in the vehicle and reused repeatedly, and while it means the vehicle needs to be able to both precisely track the outgoing shells and the target, it means that if the target veers off the timing of the detonation can be adapted after the round has been fired to get the most effective result.
For instance a standard airburst shell might be optimised to spray fragments forward to hit a target in front of it, but if the trajectory is not perfect (and it wont be) then as the fragments spray forward they will spread so detonation at 10m might allow the fragments to spread enough to hit a target that might be missed if it detonates at 5m... but the system can make these calculations while the shell is in flight.
The airburst round might also have fragments around the side to hit targets the round would otherwise miss by too far, so if the miss distance is a little high the detonation might be delayed slightly so that the target gets hit with the side fragments instead... not as effective but better than no hit at all.
The advantage of a 57mm calibre system is that it would be cheaper with no radar systems and the rounds it fires should be much cheaper than missiles though it might need 2-3 or even 5-6 rounds per target to ensure a kill, it is still better than 30-50 rounds with a 30mm calibre gun that still might miss a very small target.
To be honest if you had said even just 5 years ago that the Israelis with F-35s and all their specialist weapons and equipment were mounting mass attacks and only managed to get less Syrian SAM systems than could be counted on one hand I would have laughed in your face and told you to grow up.
The reality is that there is no 100 percent perfect air defence system, but Pantsir and TOR are pretty close.