The beach could be indefensible under these conditions imposed by the PLA to the detriment of the ROC army, but it would still be a contestable area of operations.
Its orientation of thought is that in the impossibility of producing an effective defense against the amphibious landings still on the coast, the ROC should completely leave the area of operations on the beach and hide in an urban environment without carrying out any contestation at the beach head, preventing its consolidation. It is not how it works. Whenever an opportunity arises for offensive operations against the consolidated or unconsolidated beachhead, the defender will have to act, because once the PLA action succeeds in consolidating the beachhead it may allow the triggering of subsequent operations, which, in a normal situation, they should encounter lesser resistance and achieve the strategic objective consolidated in their planning. This occurring could unbalance the conflict in favor of the PLA, regardless of the ROC hiding in urban areas.
Once the PLA fully conquers the beachhead on the coast without any challenge, the ROC is already a defeated army, even hiding in urban areas. To avoid this, even if the PLA manages to land on the beach, the ROC army must and will make attacks on this beachhead as a way of limiting the amphibious landing, making it expensive for the PLA to land on the coast, which can produce some results. depending on how they do it, they can even decrease the width of this beachhead using the initial upper fire to defeat the PLA trapped between the ROC army and the beach.
How is the ROC going to do this without air superiority?
Special camouflage techniques, deployment of inflatable baits as passive countermeasures, anti-aircraft artillery means, depending on the degree of air control by the PLA, the ROC could still use massive support from small drones (a remote but possible possibility) as countermeasures. active among other possibilities of action/reaction. The possibilities here are many, so it is difficult to deduce what will happen and how it might happen, there are many variables to consider, but the ROC has a wide range of tactics to achieve this, tactically working or not.
Let's imagine that now the ROC is no longer able to contest the beach. What comes next?
Elastic defense, offensive defensive technique, can be used normally by the echelon around brigade and lower units. In this technique, the penetration of the amphibious enemy in a selected area is allowed to destroy it through ambushes and vigorous counterattacks throughout the entire area of operations. This makes the most of the terrain and tactical surprise. The defensive position is occupied by troops dispersed in depth, eluding the enemy who initially encounters small pockets of resistance. Thus, the landing force element that enters there must be counterattacked with violence throughout your organization. Thus, elastic defense is characterized by the attrition and channeling of elements of the landing force to the interior of the advanced defense area, to then destroy it by fire in the area of engagement.
Personally I don't expect any of that. I left out how the PLA might act to avoid these scenarios.
