no no, i actually did some testing with multigrasp weapons, theres a point where they become single handed weapons for some races, the larger they are the sooner it happens, but if you multigrasp a multigrasp weapon as intended they work fine, if your not big enough to hold it single handedly you actually do get a penalty to hit chance, tested it with dwarfs humans and elfs the dwarfs and elfs were better off with smaller weapons and the humans were a bit strange tho, but the longswords won out over the two handed swords 75% of the time anyways.
mostly saying, humans CAN hit a point where multigrasp will be one handed even if the other hand is completely empty and that makes pikes and two handed swords really powerful weapons.
having a masterwork two handed sword will likely overpower the penalty for wielding it in a single hand.
its similar to how dwarfs and elfs have to multigrasp the "normal" sized human weapons to balance them out with the human skill, dwarfs are much closer due to there size and can hold them single handedly sooner.
further edit:
if you were wondering about the testing i made 7x1 rooms in the arena with obsidian (placing lava and then water) the middle spot was empty, i added a guy on each side one with legendary swordsmanship, one of them had a longsword and the other had a two handed sword and a sock in his off hand, then i filled the hole in the middle up and watched them fight to the death. i did about 20 rooms for each playable race. with the sock in the offhand the two handed sword users lost 75% of the time, without the sock they won 75% of the time.