ESOUI - STAT_CRITICAL_DAMAGE - Does this exist yet?

No idea sorry but you can do the same as at the advanced stat fragment and collect the data yourself via
function
GetAdvancedStatInfo(categoryId, statIndex)

Description how to get the categoryId, statIndex:

The advanced stats are defined via the class "ZO_AdvancedStats_Keyboard" and assigned to the object "ZO_ADVANCED_STATS_WINDOW" here:
https://github.com/esoui/esoui/blob/...oard.lua#L1080

The object contains a list where all the adv. stats are added to.
The list can have 4 different types of stats using 4 different setup functions to build the rows:
https://github.com/esoui/esoui/blob/...board.lua#L920

Code:

DATA_ENTRY_TYPE_STAT

DATA_ENTRY_TYPE_DIVIDER

DATA_ENTRY_TYPE_HEADER

DATA_ENTRY_TYPE_MULTI_STAT

where most probably divider and header do not count as they are headlines or a divider line.
So stats and multi stats count here, showing the stats values.

Here the function SetupAdvancedStats() will loop over all given advanced stats data, get cateories and build the list entries of the 4 different types shown above:
https://github.com/esoui/esoui/blob/...board.lua#L932

Lua Code:

--Get num of catgeories
local numCategories = GetNumAdvancedStatCategories()
--For each category:
    for categoryIndex = 1, numCategories do
--get num of stats in category
local categoryId = GetAdvancedStatsCategoryId(categoryIndex)
        local displayName, numStats = GetAdvancedStatCategoryInfo(categoryId)
--get stats info for each stat in the category
for statIndex = 1, numStats do
            local statType, statDisplayName, description, flatValueDescription, percentValueDescription = GetAdvancedStatInfo(categoryId, statIndex)

And here the list is setup then based on the data collected above:
https://github.com/esoui/esoui/blob/...board.lua#L966

ZO_ScrollList_CreateDataEntry creates the list entry with the list type like divider, header and the actual stats values e.g. DATA_ENTRY_TYPE_STAT or DATA_ENTRY_TYPE_MULTI_STAT

You would need to check at the data collection, by e..g using the same code in your own example function, which category and stat type etc. are used there for the critical value output and then you should be able to calculate/use it on your own by directly reading the data via

Code:

local statType, statDisplayName, description, flatValueDescription, percentValueDescription = GetAdvancedStatInfo(categoryId, statIndex)

Hope this helps