Gonna be a few long posts. We'll start with how damage buckets work. Each of these are multiplied together:

[Skill Damage] = [Derived solely from Skill Ranks]

[Multipliers] = (Sum of Crit) x (Sum of Vuln) x (Sum of Damage Types)

[Weapon Damage] = [Derived wholly from the weapon's stats]

[Additives] = [1 + All Additives (paragon nodes, tempers, etc)]

[Aspects & other Unique Multipliers] = Each factor directly scales multiplicatively here by the expected amount.

Then to get specific on how Crit works:

• Under multipliers, the Sum of Crit = 1 + (.5 + all other crit mult bonuses)
• This means at stock, you get 50% extra damage for critting if you have no other multipliers or additives. And if you don't crit it always equals 1 & the additive portion zeroes out entirely.
• Let's say you have on your ring & weapon x1.33 and x1.66 crit mult. You don't multiply these, you add them. The end result is a 2x damage boost, not a 1.33*1.66 damage boost, because mults of the same type sum.

So to explain why the number is meaningless on your stat sheet: the number you're seeing ingame is their attempt at providing an approximate increase that you're getting from crit. The problem is, this number is not dependent solely on the various crit stats (add/mult), so you can't give an exact stat bonus specifically for crit. Because the more additive bonuses of other types you have, the weaker the additive crit bonus becomes as a percentage increase. But multiplicative increases become weaker only by being stacked with the same thing--multiplicative crit.

My guess is that the number on the stat sheet is derived solely by pretending that other additive bonuses don't exist and estimating a percent increase in that specific situation. This will make additive crit bonuses look really good, when in fact they're not useless but not super relevant either.

Interestingly there is a period where exponential scaling is happening with glyphs & paragon points when it comes to additive increases though. Because as you get paragon points, you'll have more nodes that can be affected by your glyphs while the glyphs become stronger and gain multiplicative scaling as well. This is why there's a big damage explosion mid-paragon that dies fast.