Is it me, or are the vast majority of the so called 'Ultimate weapons' total letdowns? For example...Emelita's final weapon, gives an aoe heal? Emelita is a mage, by all accounts, not a healer, and New life in general is a lousy spell. It heals monsters in the radius too so...yeah. Likewise, Sharty's final weapon, the drill gloves... give Pierce III. Pierce really does not go off enough to make it that useful in my opinion. The razor gloves, with their 7 tile attack range omni magic railgun is much better. Suina's final weapon gives flash step... pretty terrible really. Crayl and Crayanne's bows PARTICULARLY sucked. Their skill is yuichiri guardian, which is a totally useless skill unless they are next to each other. Elizasleyn's weapon gives magic resist III, totally useless on a character that has seal, so they can't hit her with 'magic' period. There are a few weapons that undoubtably rock, such as Wil's legendary hammer, Lily's Demon Lord Gloves, and Phinilly's Spirit lance, but it just seems like the majority of the weapons, other then the stats, were really mediocre and a huge letdown for being so called 'ultimate' weapons.

so tell me again how a weapon that gives forcefield and got the highest stats for that char (legendary hammer) sucks

the only downside of the legendary weapons is thet they require M weapon skill, which takes a lot even with soloing dungeons which many characters are absolutely unable to do, and not even worth the hassle

I blatantly said that SOME of the weapons do rock, legendary hammer was included in that. Try reading before responding next time huh?
Likewise, I even flat out pointed out reasons why some of the weapons sucked to begin with.
And to further defeat your idea that 'the only downside' to them is the requirement... many of the weapons are also elemental weapons. Try attacking a wil o wisp, or fesp with Gaptahl's Ultimate weapon, see how far it gets you.

A question if you would. I can already synthesize(I think they are coz they require Weapon Mastery M) some of the ultimate weapons but how do you unlock the others? If it's about knowledge or sense, can you at least give a minimum amount of know/sense to unlock these weapons?

the maximum sense and knowledge required for everything is 250