Did you use the blaster rifles? They made MM6-7 trivially easy. Zero recovery time, very long range, decent damage - with such weapons you can't really lose unless you're too weak to take a little return fire.I wonder if the blasters were put in as payback for some of the insanely difficult blaster-equipped monsters in MM4, IIRC. At least, _I_ found them very difficult. Those monsters were called destroyers, terminators or something creepy like that.
Another problem might have been your character choices. If you want more challenge in MM7, try playing through the game with the other character types and without using the blasters.
These games remind me of Final Fantasy I, the original NES game, which allowed you to pick your party members from the beginning. Deviating from the recommended party made the game much more challenging (even though the final level was just completely insane regardless of the party).
