Two things about this mod I discovered while doing my own testing.
1. Power attacks:
Damage calc for items in general seems to be:
(EntityDamage + (EntityDamage * (sum of all perc_add values)) = Modified_EntityDamage,
Then if you have any DamageModifiers, Modified_EntityDamage + (Modified_EntityDamage * DamageModifier)
or more simply,
(EntityDamage * (1 + sum of all perc_add values)) * (1 + DamageModifier)
Damage modifiers are applied after all Entity/BlockDamage calculations, so things like DamageModifier tags="head" (headshot multiplier) or "wood" will be applied after.
I noticed you only have a modifier for base effects and not power attacks. All of the items with power attack modifiers have a default BlockDamage perc_add of 2. So power attacks do base damage + 200%. Using the Iron Fireaxe as an example:
Default Standard attack block damage: 30 + 0 (no perc_add values) = 30
Default Power attack block damage: 30 + (30 * (2 from power atk)) = 90
With your mod an Iron Fireaxe at Tier 6 should be doing:
Standard attack block damage: 30 + (30 * (2 from tier)) = 90
Power attack block damage: 30 + (30 * (2 from power atk + 2 from tier)) = 150
Now, this all depends on how you *want* the damages to be multiplied. With the way it is currently, the standard attack increases +200% from default but the power attack only increases 67% from default. To increase both by 200%, you could add:
<append xpath="/items/item/effect_group[@name=Power Attack]">
<passive_effect name="BlockDamage" operation="perc_add" value="0,4" tier="1,6" tags="secondary"/>
</append>
(No need to <remove> the original "Power Attack" effect, the new line will be added together with the original line in calculation for a total of 6 at Tier 6. Make sure you have tags="secondary" or this will add to the standard attack despite being in a different effect_group)
This results in:
30 + (30 * (2 from power atk + 2 from tier + 4 from power atk tier)) = 270, which is the default 90 + 200%
Now, 270 is a pretty strong power attack, so you may want to modify the "Base Effects" number, or you may just prefer it the way you have it.
2. Using <remove> first may not be necessary.
I noticed you <remove> to clear any default perc_adds then you re-add them for weapons that had modifiers, such as the hunting rifle with its 0.35. I don't believe this is necessary. If you just use <append> to add a new line, it will simply add the two lines together. I did some testing with hunting rifle block damage. Changed base to 20 for easier testing, and my Tier 6 is set to perc_add 0.5.
Shooting at a wood block which the HR gets a DamageModifier of 4 on wood. Using simplified equation:
Tier 1:
(20 * (1 + 0.35 block damage + 0 from tier)) * (1 + 4) = 135, verified ingame
Tier 6:
(20 * (1 + 0.35 block damage + 0.5 from tier)) * (1 + 4) = 185, verified ingame
So yea, doing the <remove> then re-adding for each weapon may be unnecessary. Also you have a universal EntityDamage tier multipler of 0,0.5 (+50%), but for the re-added weapons you increase by 100% (eg hunting rifle is 0.35,1.35). I would assume maybe you wanted ranged weapons to do more damage but you only added them for weapons that had them removed, but haven't added the +100% bonus to 9mm pistol or others.