Mithril, adamant etc aren't in the PHB, they're in the DMG magic items section so this doesn't come up IMC, which doesn't let PCs routinely buy anything from the DMG items section.
For the PHB armours, chain shirt is too good relative to heavier armours (except full plate) so I evened them up by increasing the max DEX bonuses as follows:
Chainmail - +3, splintmail - +1, bandmail - +2, half plate - +1.
This makes these 4 not totally worthless.
For the PHB armours, chain shirt is too good relative to heavier armours (except full plate) so I evened them up by increasing the max DEX bonuses as follows:
Chainmail - +3, splintmail - +1, bandmail - +2, half plate - +1.
This makes these 4 not totally worthless.