Quantity needs a buff.

[GAGA Extrem]

My guess is that Quantity is pretty powerful during later stages of the game, esp. when playing MP games.
Higher MP allows you to fight a lot longer and reduces WE from attrition, sieges and combat.

However, in SP you domiante the game at that stage anyway, so there is no need to pick quantity.
Another problem of the NI group is that Quality is a much better early game choise because it provides better and earlier manpower (compared to MP regen, which isn't that great during the early stage).
Quantity is also lacking an early force limit increase and (sadly) offers nothing overly interesting to naval nations.

I guess if the opener would grant some LF and NF limit and the first MP regen bonus would receive some max MP, it would be a much better choise.

 

[GAGA Extrem]

Addendum: Colonial nations can find Quantity quite interesting to overcome the oversea MP penalty modifier, effectively allowing their colonies to provide MP. Great synergy if you also build some armories there.

Here are the changes I made for my mod (note: NIs are a bit more powerful overall):

quantity_ideas = {
	category = MIL

	bonus = {
		land_forcelimit_modifier  = 0.15
		naval_forcelimit_modifier = 0.15
		global_regiment_recruit_speed = -0.15
		global_ship_recruit_speed = -0.15
	}
	grand_army = {
		land_forcelimit_modifier = 0.15
		land_forcelimit	= 10
	}
	the_young_can_serve = {
		global_manpower_modifier = 0.15
		manpower_recovery_speed = 0.10
	}
	enforced_service = {
		infantry_cost = -0.1
		cavalry_cost = -0.1
		artillery_cost = -0.1
	}
	the_old_and_infirm = {
		land_maintenance_modifier = -0.10
		naval_maintenance_modifier = -0.10
	}
	ships_penny = {
		naval_forcelimit = 15
		naval_forcelimit_modifier = 0.15
		global_ship_cost = -0.1
	}
	standardized_artillery = {
		artillery_cost = -0.1
	}
	mass_army = {
		global_manpower_modifier = 0.25
		manpower_recovery_speed = 0.10
	}

Quality for comparsion:

quality_ideas = {
	category = MIL

	bonus = {
		discipline = 0.05
	}
	
	military_prowess = {
		land_morale = 0.1
		naval_morale = 0.1
	}
	
	private_to_marshal = {
		infantry_power = 0.1
		cavalry_power = 0.1
	}
	quality_education = {
		recover_army_morale_speed = 0.05
		recover_navy_morale_speed = 0.05
	}
	oak_forests_for_ships = {
		heavy_ship_power = 0.1
		galley_power = 0.1
	}
	battlefield_commisions = {
		army_tradition = 0.5
		navy_tradition = 0.5
	}
	merchant_marine = {
		light_ship_power = 0.1
		transport_power = 0.1
	}
	massed_battery = {
		artillery_power = 0.1
	}
}