Of course you don't shoot S-300 missile here. You use S-300 radar for early detection and feed that info downstream to Osa and AK-630 CIWS. Those modern missiles were probably too much for Osa (its missiles can't hit such low flying targets), yet AK-630 would have easily dealt with them if, and this is big if, it (its gun turrets as well as its fire control radar) was turned on and warmed up and preferably trained in the general direction of the incoming missiles in time to not lose precious several seconds that the missiles were in its effective range. This is why early detection from big S-300 radar is the key.
>Also, the Moskva was never modernized. The Slava class was modernized, with the exception of the Moskva, which was not modernized at all, and only repaired and maintained.
you're again very incorrect here. Official state news with official Navy yards PR department statement :
https://ria.ru/20200703/1573824385.html
"Как сообщили РИА Новости в пресс-службе 13-го судоремонтного завода ЧФ, где ремонтировался корабль, на "Москве" была проведена масштабная работа по ремонту и модернизации."
Granted, that normally such modernization should have included upgrade of those old air-defenses, yet they didn't do it, officially - for budget reasons. (while for example its cruise missiles got upgraded from Bazalt to P-1000 thus getting land attack capability - the context of the current war clearly shows where they put their priorities, offensive capabilities over defensive, as they didn't expect Ukraine to provide any meaningful resistance, and as it happens they were very wrong :)