While the Maxim is designed to deal with massed amounts of infantry, its setup time and smaller arc make it a more mobile suppression unit and less of a mg wall unit. They are only being beaten because they don't have any units giving it proper LOS. 3 mobile units vs 1 unsupported unit should always be a win for the three or even two if used properly.
Tips:
-use 2 maxims covering each other
-Demos and or mines.
Assuming they have munis for flame nade then you should have munis for mines and demos. Maxims are fine. They only cost 15 mp to reinforce.
Any good player will blob with a mine sweeper... or use walking stuka to clear a safe path.