I will compared the Stamina sustain class, redguard versus the magicka sustain class, Breton.

Breton

The only sustain passive Breton has is a 3% cost reduction, like a Light Armor piece. So every 100 spells you can cast 3 more roughly. It is of less value the more magicka cost reduction you have so if you use Light Armor or have points in the Champion Tree to reduce magicka cost it gets weaker as you are reducing 3% out of an already reduced cost. Or if its counted first then anyway the other cost reduction effects are diminished by it.

Either way its bad... even the Altmer 10% regen does a better job as regeneration gets stronger the more you have, so the 20% regeneration from using a magicka restore potion adds with the Champion Tree regeneration, Light Armor and Racial regeneration and even the 10% from class trees or for being a Vampire.

This makes regeneration be better the more you have unlike cost reduction where its worse the more you stack.

Redguard

The Redguard starts with 10% regeneration already beating Breton and on par with Altmer.

But wait, there is more, Redguards also get Adrenaline Rush, 3% of their Maximum Stamina every 3 seconds(5 seconds next patch). This, when fully geared, translates to 1100 Stamina every 3(5) seconds.

On top of that most stamina abilities cost way less AND they get an extra 20% Cost Reduction from their respective Weapon Tree.

Conclusion

Every stamina weapon comes with a 20% cost reduction passive on top of Stamina Cost reduction being the same as Magicka. Also, stamina gets a race that can regen 1100 stamina every 3(5) seconds, calculations have deduced it counts as much as 800 stamina regen in the Character Sheet, double the Stamina regen a stamina DPS or even Tank is expected to have. Even after the nerf the number will be 500.

At current values this results in 24.000 stamina every minute. This is beyond any potion and available to anyone playing redguard making DPS have no worry about sustain and breaking any balance in PvP as Magicka builds have no way to even remotely get that via Racial passives.

Its even better than the Warlock jewelry set and ITS BUILT IN A RACIAL PASSIVE.

What the Combat Team Lead is saying about it

They are clearly noticing the Redguard, they are slightly nerfing it but it will now be 14.400 stamina every minute, way more than any potion or anything else.

Yet they said the Breton Passive is Very Powerful... and its clearly not. A 3% cost reduction at this point is nothing due to how the game changed since launch with Champion Points and such, its even lesss compared to a Light Armor piece as that also adds extra regen.

TLDR, Conclusion and Requests

With the Redguard passive being the equal of 1 potion every 15 seconds for melee builds at no cost while magicka builds are left biting the dust when it comes to sustain, why are you not balancing this now while balancing the racials?

Either remove the Redguard Adrenaline rush or make it a 10 second cooldown(would restore 7200 stamina every minute, more than anything magicka has) OR give magicka a Sustain class of equal power. First pick would be Breton as they have no damage bonuses but at this point and with race change possible any race would work.

But please do something about this because at this point it has reached a point where Magicka builds struggle to maintain resources while not even using them to dodge or block and so on while for stamina resource management the answer is always "roll Redguard". There needs to be a roll something for Magicka builds too or just remove the Redguard option but please do something about this.

Please do it now while rebalancing the racials not 2 years into the future... no reason to put this off. I also think you should just give a magicka race sustain and not nerf the Redguard further for what its worth as people are now too used to it.

As a very cheap and fast fix even a magicka wide cost reduction would work to compensate for the Stamina 20% reduction in every weapon tree.

But again, please do something about it and do not ignore this, i see too many threads about sustaining builds lately and it would not take all that many resources to fix this.