Really? How about another corvette? Or a Houti-style shore-based ASCM attack? Or a couple sub-launched ASCMs? I think its current 8-round launcher is plenty enough to handle this level of threat. A 056 is not designed or intended to defend against a determined attack from multiple fighters or ships. If you send a 056 into an operating area where it could realistically face that level of threat, you have already failed in your planning. You could extend your reasoning and ask why only the HHQ-10 launcher and not a pair of full blown 730s or even 1130s instead of just those 30mm RWS? It could easily face a multi-axis attack. Why only 4 ASCMs on the 056? What if it has to face 8 enemy ships?
That's why I said "before it has chance for replenishment". So let's say you just intercepted like 3 incoming missiles with ease. Now what? Running back home or stand down waiting for reinforcement because you have only 2 SAM lift? Or you could continuing your mission be it patrolling or sweeping an area for a sub because you have 12 missiles left to face a possible second attack.
Why not 1130 or more ASCM? Because it's a small ship and there's not enough room. 1130 essentially has same role as HQ-10 and anti-ship is not 056's primary mission. But a 18 cell HQ-10 launcher take only a little larger deck space than a 8 cell one which can easily fit on a 056 and will considerably increase its endurance when conducting many of its designed mission in low tension situation.