Personally, with today's lightweight lithium-alluminum
alloys, kevlar, graphite-epoxy materials you can make
a LEM respectably lighter.
And why launch the manned orbiter and lunar-lander together?
If the improved Ariane-5 could haul 10,000kg to the moon, use one to park a lunar-lander in low-lunar-orbit, and then a little later use another Ariane-5 to send a two-three person orbiter to the moon to linkup with it.
A more ambitious step would be to use yet-one-more beefed-up Ariane-5 to send an unmanned 10,000kg payload
to the moon to drop off a lightweight [perhaps, inflatable] dwelling on its surface.

Jacob