Question on diseases. (Tanking)

Ok, every time I ask another tank I get a different answer so I will come here to get several different insights on it.

The big question for me is are Icy Touch and Plague Strike needed. Well ok, as a rule there debuffs are very important. That said I have read several faqs.

Some say only to apply Icy Touch and Plague strike through Outbreak. While others say to keep Icy Touch and Plague Strike up at all times.

I can understand both ways but not sure anyone is better. If I use outbreak, then I get an extra death strike to provide a heal and shield. But if I use diseases, then the mob is doing less damage over all but I am not getting my heal/shield.

All of this is assuming I am on a boss. On trash I am not bothered much either way.
I don't IT if another class provides taht buff. I do PS cause of the damage done reducing it applies. If you have threat issues, IT also. But if no one provides the IT type debuff, then yes IT also (unless you are gonna die and need to DS to live).
Depends on the situation.

If you have 2 tanks attacking the same boss (Argaloth for eg.) have the other tank put up the tank debuffs as all other 3 tanks have much more easier way to put up these debuffs.

If you are the only one tanking that boss/add/mob, then I would recommend wasting the Frost and UH rune from DS to put up diseases every 1 minute.
Putting up your tanking debuffs more often than with outbreak means less death strikes per min. On farm content I would say ensure 100% disease uptime you have no reason not to, on progression content I wouldn't recast diseases (outside of outbreak) unless I know I'm not going to need the blood shield.

Let someone else take care of the debuffs in that case.
It depends.

If you have someone in the raid who can put up the equivalent debuffs, don't bother.

If you don't, then you should put them up yourself but 100% uptime is not your priority. You need to gauge the amount of damage you're about to take. If it's not much, put them up. If it's going to be a lot, don't, because you could die.

Use Outbreak on cooldown regardless.

If you want technical stuff, read below. If you don't care at all, skip to the last two lines.

A Death Strike will (not exactly) mitigate
(2 or 3)* swing_damage * .29 * (((100%-overheal%)/100) + mastery# * .0625) upfront.

Diseases will mitigate (over time)
((29/1.5) * swing_damage - (29/(1.5 * 1.2)) * .9 * swing_damage) * ((100%-avoidance%)/100)

Over time, diseases will be better (assuming nobody debuffs the boss). In the moment, DS might be better.

You're the judge.
To start, they need to be up a minimum of 50% of the time, mainly because with 2 points into Epidemic, you should have diseases up for 30 seconds at once.. and Outbreak is on a 1 minute CD.. do the math.

After that, it's your choice. Typically it's smart to reapply the debuffs in a time when the boss is doing little damage or is stunned or something like that. A good example would be when Maloriak is changing phases, or when Halfus is stunned. You can always reapply before they run out to.. just make sure it's not at the 20 second mark or something dumb like that.

Good luck!