I have found the same about the Pontic Thorakitai. They are depicted wearing mail and their name implies them to be rather well armored (just like the regular Thorakitai), yet their armour is lower than Thurephoroi, also their swords' lethality is only 0.1, not 0.13 as it the norm for shortswords. I have modded them to 11 armour and 0.13 lethality, though I consider making it 12 arm. just like the regular thorakitai and take away 'good stamina' in turn.
Other units I found underperforming during my Pontos campaign are the Cappadocian Heavy cav and Scythed chariots. The Cappadocians just have the usual problem of cav wielding spears in an overhand grip, which is useless charges. I would actually like to have them in my armies as a 'native' Pontic unit representing my realm's nobility, in contrast to all the Galatians and Hellens I use, yet Lonchophoroi or Galatian heavy cav ourperform them by far.

And the chariots... well, they are devastating, but not only against one's enemies, but even more so against own units. After they have taken some losses and I have retreated them behind my own lines, they just run amok out of nowhere, despite their morale being 'eager' or 'impetous'. Afterwards, they always charge my own general or cav units.