Frisians can be upgraded to Light Cavalry or Heavy Infantry...their Light Cavalry is about as strong as that of the Germanic factions, IIRC, while Frisian Heavy Infantry are a little weaker and slightly cheaper than Duguths (200 Weapon Proficiency for the Frisians vs 230 for the Duguths I think). However, the Frisians' strongest heavy infantry unit is only Tier 3 while Duguths are Tier 4 so the Frisians can be trained up faster and then they can give even the top-tier infantry units of other non-Germanic factions a run for their money. AFAIK, Frisians can only be recruited from Cymensoraham and Buegan Ora.
The Picts have a reasonably diverse unit tree, their Fuider skirmishers can upgrade to Eite Fuider elite skirmishers while their Each Raidh light cavalry can upgrade to Airig heavy cavalry. Pictish units hit harder than equivalent tier troops of other factions with their top-tier heavy infantry and heavy cavalry having a Power Strike of 5 but, on average, they're more lightly-armored than other factions and even their top-tier units spawn with a mix of mail, scale, some varieties of medium armor, and even standard tunics that you start out the game with (!...at least the Airig, not sure about the heavy infantry). If your character has a high enough level to train your troops to the highest level (mid 20s, IIRC) and all your party members as well as you have at least a moderate level of Trainer skill (4-6) then you should have no problem rolling over other armies of more mixed quality with a high-tier Pict army, but on a more level playing field the Picts are the sort of troops that can kill fast and die fast.