Squishy tanks... is it me or them?

[ArianeEwah]

I feel like it doesn't help that there's a buff cap on the party list of ... what is it, four? and that's almost always taken up by protect. Then you've got maybe adlo, medica II... blocks you from seeing the tank's de/buffs, which are an important gauge of how much damage you can expect.

You can actually increase this cap in your options, from 5 up to 10 buffs/debuffs. If you focus target the tank, you have an even easier time to see all buffs/debuffs on them (with duration), while you DPS the boss/mobs.

- [...] Some take this too far an heal themselves, looking at you paladins (and some red mages). These same tanks usually do bosses in dps stance and switch the burden back onto you.

I acutally don't mind that PLD heal themselves if that means I can DPS more as healer. Esp. in big pulls, healer AoE DPS is higher than that of a tank and depending on how many enemies there are, and how long it takes to beat those, you don't have enough oGCDs+regen to keep your tank alive. If the tanks sacrifices some of their lower DPS to keep up healer DPS, I am pretty okay with that. (But damn you RDM spaming Vercure on the tank with excog applied.)
So, I wouldn't count them all to the kind of tanks that don't know how to tank in DPS stance.

b@Topic:
There are certain factors that define the "squishiness" of a tank.
1. The gear: While in HW and SB tanks can't equip any "Disciple of war" gear anymore, below level 50 they still can. I think that is the biggest factor, because even lower item-level tank gear is sometimes stronger in defense (esp. magic defense) than "Disciple of war" gear.
Personally, I think it's easier to heal a tank with high defense and low HP than a tank with low defense and high HP.
Overwise the higher the item level the better (and of course HQ gear).
2. The skill: If you get an experienced tank, who actually rotates through their CDs instead of using all the same time or none, gear becomes a minor factor. Even an undergeared, yet experienced tank will be easier to heal.
They dodge AoE, know fight mechanics and act accordingly, pay attention to the party, and use CDs at crucial times.
Sometimes you wouldn't even notice that they switch to DPS stance at boss fights.
3. The DPS of the party: This is actually the hardest to tell at the first glance. Your tank checks every gear, sees that they are well-equiped, and does a big pull. But somehow the mobs don't die, your oGCDs already used, the tank is running out of CDs and taking serious damage. Sooner or later even your strongest single target heals can't keep up with this many mobs. In this case neither the healer nor the tank were bad/squishy, it's the DPS not doing the damage they should. Mobs might get buffs the longer they live, there are mechanics that can hurt the tank (like final sting). If your DPS doesn't know what they gotta do, even a great tank/healer combo can shatter.

[Ekimmak]

If you focus target the tank, you have an even easier time to see all buffs/debuffs on them (with duration), while you DPS the boss/mobs.

I tend to focus target the boss, so it doesn't blindside me if he starts winding up a big aoe/tankbuster while I'm specifically healing someone.

[Yeol]

I tend to focus target the boss, so it doesn't blindside me if he starts winding up a big aoe/tankbuster while I'm specifically healing someone.

You can see the cast bar in enmity list now
Just move it somewhere where you can see it. It is very useful to see the cast of multiple targets.