Is asking a tank to use his enmity+ buff rude?

[Gamemako]

I disagree, but it depends on the party.

One cast of Holy will do as much damage as you do over an entire pull from Sword Oath. The loss of just one GCD alone to additional healing from Sword Oath makes it disadvantageous. I will try to show this mathematically.

Let's assume you need 4 uses of Flash in Shield Oath to maintain aggro through the pull. Because the full 50% from Shield Oath is given (Flash is not damage-based), this is 6 Flashes in Sword Oath, a loss of 5 DPS-seconds. We will assume 6 targets for the purpose of this analysis.

Shield Oath potency per second: (150 + 200 + 260)/7.5 + 100/3 + 6*250/25 + 300/30 = 184.67 base * 0.8 = 147.73 potency per second
Sword Oath potency per second: (150 + 200 + 260)/7.5 + 100/3 + 6*250/25 + 300/30 + 50/2.32 = 206.22 potency per second

DPS gain per second: 0.400 DPS-seconds per second

Time to equivalence: 17.5 seconds

Assume 40-second encounter duration (probably overestimate). Total DPS gain: 9 DPS-seconds -- 1329.57 potency.
WHM holy: 240 potency * 6 opponents * 1.3 maim & mend * 1.1 cleric stance * ~1.4 stat and weapon damage differences = 2882.88 potency.

If WHM loses just one GCD to healing, you're well behind in total DPS.

This isn't the most exacting analysis, but it should give you a good idea of why Shield Oath is a better option for mob situations. Start in it and stay in it. When it comes to bosses... well, that jelly does probably 200 DPS and you need no Flash, so over the duration, healer loses one GCD per 25 seconds. PLD gains 10 DPS-seconds in that much time, or around 1350 potency. Holy would be less than 500 against one target. Either way, Sword Oath wins out in situations with few targets and low damage rates.

//EDIT:

How much does Sword Oath actually add for total Dmg?

I've had the occasional PLD want to "make the run faster" but given how much extra time I have to spend out of cleric stance healing them I question whether the net increase is actually positive.

Sword Oath adds 50 potency per autoattack. In total, it is 40-45% more DPS over Shield Oath depending on the number of opponents (inversely proportional due to CoS contribution).

[Lucavern]

One cast of Holy will do as much damage as you do over an entire pull from Sword Oath.
SNIP

I don't recall at any point stating that I explicitly use a WHM as my healer. Your math looks right, and I agree about the dps gains comparing PLD dps vs Holy usage. Things that I don't think you are calculating on however: MP conservation/usage to keep that rate of Holy usage throughout entire run (I've seen WHM try to do this and be OOM halfway through run when chain/multi-group pulling). I've also done runs where I had a SCH as my healer who stayed in Cleric Stance the entirety of the run and let Eos heal, and only needed to cast 1-3 heals himself throughout the entire run.

As I said earlier, I feel that it really depends on the party composition, and the individual players involved. At this point however, we have gone completely off-topic from the OPs post. I'll continue this discussion in a different post if you want Gamemako, but I don't want to further derail the thread.

[Gamemako]

I do not believe that is the case, because if it were, then a Tank in Shield oath/Defiance would be generating more enmity than a Tank in sword oath/not in defiance.

It does in fact generate more enmity than a tank without. This is necessary for PLD in particular, who would otherwise be forced to do nothing at all when not main-tanking.

What he's referring to is that it takes much more STR or DET to make up for weapon damage. Damage, and by association, threat, does not scale for a tank as quickly as +1 on weapon.

I believe that would be misleading. There is only one weapon upgrade to make in Coil and only one weapon upgrade to make for Titan HM. You are comparing ilvl60 to ilvl70 or ilvl80 to ilvl90. These are not great jumps; the difference in STR scaling is minimal between the two (2.5-3%). This would not change your stat allocation decisions. One way or the other, though, you can hold enmity on ilvl90 players going full blast when wearing ilvl55 gear, so if you're losing enmity, it's your fault. This large buffer is why tanks often forgo relic+1 when other options are available.

I will note, however, that I did interpret that player's comments to be the (somewhat common) misconception that "increased enmity" is a flat bonus rather than a multiplier.

I'll continue this discussion in a different post if you want Gamemako, but I don't want to further derail the thread.

Might be worth doing later.