How can they contest the landings if they are all hunker down in the cities preparing for urban combat? If they are not contesting the landings, the PLA can land with giant inflatable rubber duckies for all the difference it would make.
Big ticket LHDs and LHAs are door kickers designed to smash open the beachheads as quickly and as effectively as possible. After the beachhead has been secured and breakout achieved, follow on forces can land via whatever means necessary while the LHDs and LHAs are free to return to port because it’s game over by that point.
If any die hards try to hold out in the cities, the PLA can send it as many troops as needed.
And Taiwan’s reservists will just be live target practice for the PLA if they are stupid enough to show up given how pathetically little training they get.
Look at the distances. You've got urban areas a maximum of 15km from any beach.
The beaches will be within view of any defenders holed up in a city.
The would act as spotters for artillery, mortars and missiles to range the beaches.
But I don't see that being enough to stop the beach landings.
So yes, the PLA can send in as many troops as needed. But die hards holding out in cities will take time to clear out.
That is the biggest risk because if it drags on for weeks, it invites US intervention.