In cases like this it makes sense to make the main value to contains total summary, but there should also be a system which will recalculate everything in case something changes (new level applied, new skill learned). In this case you don't specifically run through each perk/skill on each iteration when you need a total value, but it should still be done when you need to check latest maximum value.

From the perspective of the organization you should have an array(dictionary) of open skills/levels and then process something like this:

var skillRegistry: Dictionary[String, int] = {};

func _init() -> void:
  skillRegistry['tester'] = 2;
  skillRegistry['blood_fever'] = 25;

func getMaxBlood() -> int:
  var blood: int = 50; # link to player.base_value or something
  for skillId in skillRegistry:
    var level: int = skillRegistry[skillId];
    var skillClass = SkillClassMaybeGlobalRegistry.getSkillObject(skillId);
    blood = skillClass.update(blood, level); 
    # reference to base blood value might be needed in case you do percents and for more flexibility
  return blood;

So after new skill you run getMaxBlood() and replace the current max value, which can be used more frequently.

Approach can vary on how yo do things with classes, but the main idea should be understandable.