The Monk Temple

[Almalexia]

That what he means by linear - this is pretty standard terminology in MMO/statistics. Each point adds the same amount of actual dps.
Say you do 100DPS ignoring crit rate. 1% crit adds 0.5 DPS whether you are at 0% crit or 99% crit rate.

What Rapiso is calculating here is the DPS per crit percent, not necessarily crit rate as a stat. Still, I am not convinced his example is accurate for FFXIV.

To examine this, let's use the BLITZBALL formula for calculating WS damage:

(Potency/100) x [((0.0032 x STR + 0.4162) x WD) + (0.1 x STR – 0.3529) + ((DTR – 202) x 0.035))] x (1 + (0.5 x (0.0693 x CRT – 18.486)/100))

Our simulation will use a potency of 100, WD of 40, STR of 400, DTR of 250.

When CRT = 400--or a crit% of 9.234--the result is 114.2157144
When CRT = 500--or a crit% of 16.164--the result is 117.9986316
When CRT = 600--or a crit% of 23.094--the result is 121.7815488

Every 100 CRT improves crit% by 6.93, as well as average WS damage by 3.7829172. The formula suggests both the crit% and the damage outputs are linear; we can easily predict what the average will be at 700 CRT or 1000 CRT. You gain exactly as much damage per crit% as the crit% before it. The only way you start losing returns on CRT is when we run into a hitherto unknown crit cap.

[Rapiso]

What Rapiso is calculating here is the DPS per crit percent, not necessarily crit rate as a stat. Still, I am not convinced his example is accurate for FFXIV.

...

The only way you start losing returns on CRT is when we run into a hitherto unknown crit cap.

Yes and :
((117,9986316/114,2157144)-1)/(16,164-9,234) = 0,0047793 < 0.005
((121,7815488/117,9986316)-1)/(23,094-16,164) = 0,0046261 < 0.0047793 < 0.005