Let me try another way of saying this...
The Archetype entry specifically says "Weapon and Armor
Talents". Martial says "You gain Armor Proficiency in ALL armor and shields common to your starting nation" which to me is clearly short-hand for saying:
- Armor Proficiency, Light (starting nation)
- Armor Proficiency, Medium (starting nation)
- Armor Proficiency, Heavy (starting nation)
- Armor Proficiency, Shields [all because there is no sub-division of this talent]
The wording for Arcane and Expert also seem to back up this reading.
If the intent is that the Martial Archetype breaks the Talent definition (for Shield Proficiency) then it needs to be called out
very explicitly. I'm pretty sure this is the only case anywhere in Arcanis where something grants only part of a Talent (eg the Talent normally gives "all" of something while the Path/Background/whatever only grants a few of something (instead of all)).