Doesn’t the small size make it more impressive that the Texians held out for so long?

Well, all that remains of the alamo is the chapel and a residential unit.

It was originally a quickly fortified missionary complex which is a large plaza surrounded by walls.

You may have misunderstood what you were looking at. All that is really left is the chapel. It’s just a church sized for a few hundred people. All of the houses, offices, barracks, work rooms, stables, storehouses, defensive works, etc, etc are all gone. They were left to rot when the place was abandoned for a decade or two, then cleaned up when there was an army present, heavily damaged in a certain famous battle that you might remember, partially repaired by the occupying Mexican army, then burnt down again as they left. Only the chapel remains, and that’s because the walls were built of limestone blocks four feet thick. They were too solid to tear down and couldn’t be burnt.