Dev Team, you screwed up.

[Flana]

Not implying BLU can or should be a tank, but I'd be remiss if I didn't point out Mighty Guard adds emnity to every skill the Blue Mage uses while reducing damage taken. I've seen Blue Mages paired up with level 70 tanks where the tank struggles to hold agro against the level 50 blue mage. Additionally Blue Mage has The Look which is an exact replica of Overpower, meaning that the only real pieces Blue Mage is lacking to be a tank are defensive cooldowns, and the ability to wear tank armor to increase defense.

Again, I don't think the job should be a tank, but if sometime in the future they decided to turn it into one, a couple of the keep pieces already exist for it to fit into that role.

Which is why I compared it to Summoner and Titan-egi. Titan-egi passively takes reduced damage in a huge amount of circumstances due to be being a pet. He also has an actual tank cooldown (Earthen Ward is literally Rampart with a longer cooldown). His AoE and basic skills have a permenant increased enmity effect on them along with the fact Rouse + Enkindle generates an insane amount of enmity. I'm not joking when I say he can generate an absolute massive amount of threat with Enkindle.

Does that make Summoner a tank?

No, for the same reason I don't think BLU is a tank either. The only real 1-to-1 is Mighty Guard being a tank stance. The Look, along with most BLU spells, are still spells with a cast time. You have to stop and cast all of them. This creates problems down the line by pushing everything to the end of the GCD. In my earlier post I mentioned if a BLU wants to throw on tank stance and save a party wipe, it takes them twice as long to do so over a real tank at a minimum. Might Guard and your next spell have to be cast before they can take effect. Any tank can hit their stance and immediately ogcd if need be. Even if they don't have one, weaponskills trigger at the beginning of the gcd. Overpower will always be faster than The Look. They're worse in every way to a real tank, which is why I don't believe they count.

Neither BLU nor SMN are designed to be tanks, but they have enough tools to function as a stopgap in the absence of a real tank. I don't think that stopgap ability makes them a viable replacement is what I was getting at.

Edit: Going back and looking at my post, I realize I only refereed to Mighty Guard as "tank stance" once, so I apologize if it seemed like I was deliberately ignoring it. I should have been more explicit and mentioned the ability by name.

Explain to me in which content a Summoner is tanking in place of a tank and a Red Mage is the healer.

I can reverse this question as well. Show me in which content a Blue Mage is taking the place of a real tank or healer. I mean synced coil or extreme primals with a real team comp. Blue Mages only being used to replace the tanks or healers, and not 8 Blue Mages memeing the content to death because White Wind explodes in power the more Blue Mages you add in. If it can't function without exploiting a full party of BLU for White Wind sheninagins, then it isn't a real replacement for those roles. And for every one of those that do clear, how much effort was put in to mitigate having a BLU over a real job?

To answer your question: Summoners have tanked at least O1S, Ridorana, and Rabanaster in this expansion just off the things I've seen from Reddit. I'm positive they've done more in Heavensward and Stormblood, since Titan-egi can work as a tank as long as he doesn't get one shot by a tankbuster. He even has a cooldown you can manually pop to help out with that.

I'm also going to agree with Valdegarde, when I was raiding on Red Mage there were several times I kept the tank or healer alive long enough to stabalize, thus filling out what might be considered the "off-healer" role. Really since most content can be cleared with a single healer, off-healer doesn't really amount to much if the group is on top of it... But that goes back to my earlier point. I doubt anyone will ever one-BLU O8S for example. It's not possible. Blue Mage by design can not replace a real healer like White Mage, Scholar, or Astrologian.

However, I do not believe Summoner is a tank nor Red Mage is a healer. Just like I don't believe Blue Mage is either of those things either. It lacks too many tools to efficiently fill in the role compared to any other choice. You wouldn't BLU because it's the right choice for the content, you'd do it because you can. Just like I can tank random stuff with Titan-egi, but choose not to.