Im sure the Taiwanese would kill many many invading Chinese. But eventually they would simply be overwhelmed by numbers.
Shortly after the Chang & the KMT withdrew to Taiwan and a few smaller islands (Quemoy & Matsu), the PLA attempted to take one of the smaller islands. They got ashore, but that’s about it. Their supply ships got interdicted and the entire invasion force was rounded up for lack of food, water and ammunition.
Admittedly the PLA improvised the whole thing. But on the other side the KMT forces were pretty demoralized and they still managed to defeat the enemy.
Seaborne and Airborne invasions are tricky things. The little things can lead to disaster.