You were there with them ? What I understand is that they didn't even detected the attack which is very unlikely if the systems were operated. At least those 35mm should have opened fire at the last moment. The most likely is that they were turned off and the crew was sleeping.
Those batteries are around defended rafinery, what mean they are on duty. If they sleep, when they are on duty, this is a problem of discipline. If they are working and didn't see them, than it could be, that the crews are bad at training or they are bad at maintaing radars and they are not working properly.
IADS means early warnings too. So they need radars at borders to detect the entry of cruise missiles into the territory and put on combat duty all the air defence systems if they are not which they didn't. The best way to do so is put many small radars in places were cruise missiles have advantage over your air defence line mountainous areas or deserts were there is no one.
That's what russia did in Syria. They deployed 1l122 there. But they can also deploy more Kasta than a small country as they produce them and they are cheap for them. Syria is full of such radar around Hmeimim ro provide early warning.
Of course. IADS means integration of all air defense components including air force into one working organism. They are all sharing their pictures and higher levels coordinate the work of all units, that engagemns are optimal. It's not good if three batteries engage the same target, while the rest are flying through.
Absolutely Russia send many different radaras to test them in real combat conditions. Also having more radars at different locations is a kind of protection against anti radar missiles as you could divide transmiting of radars in short time period, that anti radar missiles could not lock on radars. Also it works against jamming and increase precision in detection by triangulation.
Saudis have radars and SAMs at the border with Yemen as there is war and Houtis often launch drones and missiles into Saudi Arabia. Why they didn't detect is question for Saudies.
They are helped by russians for their airdefence. Very unlikely it was alone. Even with a baterie they would need to destroy tens of missiles in matter of 1 minute.
Yes, Russians help Syrians with informations, rebuilding air defense and training crews. But they could still hardly help them, when they did something stupid. For sure Syrians know, they should not divide batteries, but they did. Most probably their problem lies in fact, that they have too small number of such complexes to protect all needed objects all around Syrian territory. Battery of Pantsir have 6 TELARs with 12 missiles each. Every TEALR could engage 4 targets simultaneously, what means Pantsir battery could engage 24 targets simultaneously. But when the missile hit the target, one missile channel is free and you could launch another missile. This mean Pantsir battery could theoreticaly launch 72 missiles at 72 targets in one salvo. Than they need to reload. 72 drones or cruise missiles is quite a big number and they cost a lot of money.