let's do a short numbers game:
We use the example of a DK here because it doesn't inherit a source of purge in his class toolkit.
In non cp both break free and efficient purge cost 5400 stam/mag.

CC immunity is 7 seconds that means in 70 seconds we can only break free a maximum of 11 times (10 if we aren't stunned at 0 seconds) assuming we actually get stunned on cooldown.
We'll use the 10 purges so we get even numbers here it won't matter in the end.
That's 54,000 stam spent over 70 seconds for break free.
Meaning if we had to completely get that amount of stam via regen and we have no stam at the beginning we would need a stam regen of:
54000/35 (regen happens every 2 seconds)
Which results in ~1500 stamregen required to keep up the break free for 70 seconds.

But we don't have 0 stam when this experiment starts right?
So now we use a 15k stampool which we directly subtract from the 54,000 required stamina resulting in 39k stamina required and which brings our stamina regen requirement down to ~1.1k regen.
Most builds feature a minimum regen of about 700 without any investment. So now we only have to reach 400 regen via other means which are different for all specs but exist for each one of them.
For a DK that would be helping hands (restoring 990 stam on casting a earthen heart ability like fossilize))
And battle roar which returns 46 per ultimate point up to the cost of the ultimate used.

As we want to stun the enemy as often as possible we'll also use fossilize every 7 seconds resulting in 9.9k stamina over 70 seconds or 280 stamregen.

So we need 120 more regen and that's easily covered by helping hands even when only gaining the 3 ult per sec from light attacks as it results in ~240 stam and mag regen.

We also haven't covered the useage of tri pots (8k resources every 45 seconds or in the long run 355 stam and mag regen.

Summing this all up leaves us with: 1.5k stamregen and wow this means we can even sustain the break free if we start with 0 stamina or if we start with 15k stamina we can use 400*35 = 14000 stamina as we want to, while still being able to always CC break.
For you this means 26 seconds of sprinting if you're using 5 light and have the grace passive unlocked.

Also CC break works all the time and doesn't scale with the number of enemies you're facing because the Cc immunity is on you which means no matter if 1 or 70 enemies you can't be CC'd more than once every 7 seconds.

Now let's head over to something that does scale with the number of enemies you're fighting while also loses effectiveness when facing multiple people and is tied to luck.
As explained in an earlier post you often have 10 negative effects on you depending on your enemy you have more than 3 strong dots on you but purge only helps vs 3 of them and for every additional enemy the number of dots on you increases further and you can still only remove 3 of them.

Let's use the same example as before: fight over 70 seconds, purging every 7 seconds, total purges =10
Cost for this are 54,000 magicka.
The total amount of negative effects removed is 30.

We will need 1.5k magregen to keep up with purging every 7 seconds or 1.1k if we have a starting pool of 15k magicka.
But here comes the issue, we also have class skills we have to use as a DK and they come with a magicka drain, namely volatile armor and cauterize, both skills are required to be used as not using them puts us at a direct disadvantage.
Volatile costs 2700 magicka every 20 seconds and cauterize costs 2160 magicka every 15 seconds resulting in a drain of 558 magickaregen (cost*2/druation).
This increases our need for magicka to 1.6k and 2k magregen depending on the scenario.

However there's no such thing as helping hands return in a DKs toolkit, but helping hand stays the same so 480 regen here:
Resulting in a need for 1,15k or 1.55k magregen again which we have to get via direct regen, remember how we had 700 regen as a base in the other example?

Well even with pots we need ~100 or 400 magregen to sustain a purge every 7 seconds.
See that we're not even talking about having mag to spare anymore?

Which leads us to the next big issue purge isn't as reliable as CC break because CC break directly counters the CC and isn't attached to any luck, you use it and you're no longer CC'd. Purge is completely different here in the example with 10 negative effects out of which 3 dots are the chance to have them removed in one go is less than 3% for one single cast, for 10 consecutive casts the chance is 2,0*10^(-16) to always remove the 3 dots you want to remove.
Not even winning the lottery is connected with such a small chance of success.

And that's just the example for 10 negative effects, we haven't even covered the issues when you're facing multiple enemies who all put additional dots on you up to a number that you're unable to remove them all even when spamming purge till you run out of resources.

The sustain numbers shift even further in favour of CC break when we look at Cp as you can easily reduce the cost of CC break via CP to 4k but none for purge while the number of debuffs increases in CP due to siphoner and tactician.


//granted those scenarios use generalizations and ignore some things to have an easier application of the topic//