Diirk said:
At 10 strength a light load is up to 33 lbs.. 12 str <= 43 lbs, 14 <= 58 lbs.. so I guess it depends how strong your psion is and what else you're carrying. But if 15 lbs is such a big deal, that suggests you have a quite low str (10?), so why are you wading into combat with a 2h weapon? The -1 to hit with the buckler isn't fair anyway, as then the buckler ac bonus wouldn't apply. He probably had in mind using a one handed weapon, or even no weapon at all. And like, using psionic powers or something.
Obviously you prefer not to play your character that way, but its fairly obvious it can be a good way to play it, as can be shown by you spending 1/5th your daily allotment of pp on boosting your ac by 10? for most of the day

Besides, it frees you up to pick different powers. (Which is the main reason I did a similair thing on my sorceror)
Have you actually played the encumbrance rules in your game? Or do you blow them off?
Everything in DND weighs a LOT.
A simple waterskin: 4 pounds.
A bedroll: 5 pounds.
A character with a 10 Str carrying a belt pouch, a bedroll, a single days trail rations, a waterskin, the Mithral Chain Shirt, the Mithral Buckler, and a Greatsword (which in DND is carrying next to nothing) is carrying 37.5 pounds and is in a medium encumbrance category by 4.5 pounds.
It is extremely easy to get into a Medium Encumbrance category in DND, even if you have a reasonable Strength. My psion has a Strength of 14, but even at 58 pounds for a light load, using the Mithral Chain Shirt and Mithral Buckler is over 25% of what she can carry and drops the rest of her allowable equipment to 43 pounds.
And for Mithral Armor/Shield to be viable for any character, let alone a psion, that character needs to allocate a lot of funds towards that in order to have a fair chance of not getting hit in combat. Funds which can be better used to enhance other abilities or shore up other weaknesses.
Plus for any character class that does not have any armor/shield feats, a Mithral Chain Shirt is the best armor that character can get without sacrificing to hit. Once you get to Mithral Scalemail or heavier armor, a character without those feats will be taking a armor check penalty to hit.
My psion is an Egoist. Her strengths lie in boosting her AC and other physical abilities. It would be dumb to not play to her strengths.
Ditto for other psions. A Kineticist should attempt to blow opponents away. A Telepath should attempt to sway opponent's minds, etc.
Finally, even the other psion in our group (Fighter 2 / Kineticist 4 / Elocater 1) who is wearing a magical Breastplate still uses up PP in every combat boosting his AC and other defenses. He uses Force Screen, Concealing Amorpha, Biofeedback, and/or Precognition, Defensive nearly every combat.
But in order for him to wear armor all of the time (and qualify for the Elocater class early on), he had to give up PP and manifester level as well. Nothing comes for free.
He has 42 PP at 7th level whereas my character had 58 PP at the same level (at 8th level, he will have 55 PP whereas my psion has 76 PP and the delta will be even greater). So yes, you can go the armor route, but the fact that you have fewer PP to begin with (about 25% fewer in this example) can easily make up for the PP spent on AC when a psion does not wear armor.
Plus, my higher AC psion gets hit a lot less often and is less of a burden to the party Cleric. You can have all of the PP in the world, but if you are dead, they are not going to help you.