With the version of Java that I use, the column weights would be: 0.0,
3.0, 4.0.  What docs "say the max in each"?  You can run a small program
like the following to determine the actual column weights.

import java.awt.*;
                                                                               
 public class Test {
   public static void main(String[] args) {
     Frame f = new Frame();
     GridBagLayout gbl = new GridBagLayout();
     f.setLayout(gbl);
                                                                                 
     GridBagConstraints gbc = new GridBagConstraints();
     gbc.fill = GridBagConstraints.HORIZONTAL;
     gbc.weightx = 0.0;
     f.add(new Label("comp1"), gbc);
     gbc.weightx = 3.0;
     f.add(new Label("comp2"), gbc);
     gbc.weightx = 2.0;
     gbc.gridwidth = GridBagConstraints.REMAINDER;
     gbc.weightx = 1.0;
     f.add(new Label("comp3"), gbc);
     f.add(new Label("comp4", Label.CENTER), gbc);
     gbc.gridwidth = 2;
     gbc.weightx = 0.75;
     f.add(new Label("comp5", Label.CENTER), gbc);
     gbc.gridwidth = GridBagConstraints.REMAINDER;
     gbc.weightx = 4.0;
     f.add(new Label("comp6"), gbc);
     f.pack();
     f.show();
 
     double [] columnWeights = gbl.getLayoutWeights()[0];
     System.out.print("Column Weights =");
     for (int i = 0; i < columnWeights.length; i++) {
       System.out.print(" " + columnWeights[i]);
     }
     System.out.println();
   }
 }

The weights of the components indirectly affect the widths of the
components.  The weights of the components are used to determine the
column weights.  The excess width is distributed among the columns based
on the column weights.  The widths of the components are the widths of
the columns that the components occupy.

In you example (assuming that GridBagConstraints fill is properly set),
the width of comp4 is the width of the 3 columns of the grid and the
width of comp5 is the width of the first two columns.