My initial thought is that this is unbalanced. A +2 save is the equivalent of a Talent point. Saves are already so high in the system because you get bonus Resistance at level 3 and 6. Save DCs are also very low unless you cast an expensive high mana spell.
With the Iron Spell Resistance optional rule an Archeon at level 3 will have a Base +3 Will save, +1 from WIS, +1 Resistance level 3 = +5, if they take the talent Spell Resistance thats another +3 for a +8. That means they save against 7 mana spells on a 9 or higher d20 roll.
If that same Archeon is in Iron Full Plate (+3 spell save) and using an Iron Tower Shield (+2 spell save) they have a +13 Will save making them effectively immune to magic at level 3. They need to roll a 4 on a d20 to save vs 7 mana spells. That’s crazy IMO.
The hinderance as written is that their Max Dex bonus is 0 instead of 1. AC 10 +8 Full Plate + 4 Tower Shield +0 Dex TOTAL AC 22. The extra weight means 100 lb Full Plate, and 90 lbs Shield. With a STR of 16+ that is a Heavy load, but if their speed is 30′ that only drops them to 20′ the same as a Medium load.
And we haven’t even gotten into Legacy Items yet. The world is already so unfavorable to mages. Iron arrows already stop magic. This system goes too far IMO.