You are reading it incorrectly. The Large Sized 2-handed weapon according to RAW for you is a HUGE sized 2-handed weapon.
Weapon Size Every weapon has a size category. This designation indicates the size of the creature for which the weapon was designed.
A weapon's size category isn't the same as its size as an object. Instead, a weapon's size category is keyed to the size of the intended wielder. In general, a light weapon is an object two size categories smaller than the wielder, a one-handed weapon is an object one size category smaller than the wielder, and a two-handed weapon is an object of the same size category as the wielder.
Inappropriately Sized Weapons: A creature can't make optimum use of a weapon that isn't properly sized for it. A cumulative –2 penalty applies on
attack rolls for each size category of difference between the size of its intended wielder and the size of its actual wielder. If the creature isn't proficient with the weapon, a –4 non-proficiency penalty also applies.
The measure of how much effort it takes to use a weapon (whether the weapon is designated as a light, one-handed, or two-handed weapon for a particular wielder) is altered by one step for each size category of difference between the wielder's size and the size of the creature for which the weapon was designed. For example, a Small creature would wield a Medium one-handed weapon as a two-handed weapon. If a weapon's designation would be changed to something other than light, one-handed, or two-handed by this alteration, the creature can't wield the weapon at all.
Basically it goes like this:
Jotungrip allows "appropriated sized" THW weapons meaning if you are medium you are allow to wield it "1 hand" as if it was a one handed type weapon with a penalty of -2, which if you couldn't do.
Massive Weapons allows "Inappropriate sized weapons" to be wielded in frame work you suffer a -2 for each size grade too large of equitable weapons example...a "Large Dagger" is a One Handed Weapon to you but you still suffer a -2 for its size it's not meant for your "size" if it's a large sized long sword you suffer a -4 cause technicality is it's a "large two handed weapon" but meant for a "large" character if you try to use a large sized great sword you take a -6 meaning the large size great sword is the finale.
Another example: huge sized dagger is a "Two Handed Weapon" meaning you take a -4 to wield it as such cause it's not a proper "weapon" it's not BUILT for your size it deals the "Large Size Dagger Damage" no matter what size grade you are....BUT this ability does not make them appropriate size for you, you negates penalties meaning JotunGrip still only applies to the "Two Handed Weapons of your Size Grade built for your SIZE GRADE"
Light = 2 sizes grade smaller
One Handed = 1 size grade greater
Two Handed = even size
Nothing goes past this line EVER
Smaller sized weapon also grade down so a Small sized Dagger is -2, a Tiny sized Dagger is -4, a Small size Long Sword is -2, Tiny sized Long Sword is -4, Small sized Great Sword is -2, Tiny sized Great Sword is -4.
Note there is nothing smaller than tiny but if you are a large sized character it would be a -6 as the weapon would be 3 grades smaller thus -6 if huge sized used a tiny sized it be a -8. The reason is because of hand size and handling too small of pummels/hilts or weight balances etc. the size of the weaponry itself compared to your own size category is what counts here.
Large Dagger = One handed for mediums with a -2 penalty
Huge Dagger = Two Handed weapon for mediums which is a -4 penalty
Large Long Sword = Two handed for mediums with a -2 penalty
Huge Long Sword = Unusable it's past the Two handed grade upon size up
Large Great Sword = Unusable
Bastard swords are a special case weapon they ONLY turn one handed if you are trained in them this is a special case they are Two Handed Weapons without the feat thus
No feat = unusable for a medium char using a large bastard sword
Feat = using this over sized weapon is -2 as Bastard swords turn into a "One Handed Weapon" and by RULES One Handed Weapons CAN be used two handed as the same of normal Two Handed Weapons while Light Weapons cannot but used 2 handed bonus