Hey guys, so I've been playing a ton of Rune Fencer and learning the ins and outs of this job. A lot of what I'll be saying is probably going to be a repetition of something you may have heard or already know, but there seem to be a lot of people who don't seem to get how to really make RUN 'work', let alone as a tank.
First, some clarification: This is at 99, doing adoulin content (WKR's and Delves, specifically). I'm not especially well geared-- was in mostly sparks gear for a while but recently upgraded to the new homestead and tier 6 peacekeepers gear (head, body, boots of schneddick, hands of weatherspoon (for cure+% mostly), and one of the WKR pants I think, can't recall which specific one). I have some pretty good accessories including my JSE cape. So roughly 117 level gear, but not totally decked out with the best. However, you'll see that it's not that important if you play smart.
That isn't to say that good gear isn't important, of course; I saw an appreciable difference in how strong I was in fights, how much easier I held hate, and the general ease of keeping myself alive and buffed after upgrading.
Also: This is all with /RDM on. I haven't gotten to mess around with other subs as much (mostly due to lack of having most appropriate ones leveled), but I really haven't had much need to. RDM gives RUN a ton of flexibility, and fast cast and convert are really handy when you burn through MP. Looking at things, I'd be able to argue that BLU is also a decent sub; potent heals, cocoon, some other nice attacks to generate hate. I haven't actually tried it, though. Don't bother subbing BLM for the magic attack bonus; it's not really worth it. DRK might be okay but again, it kind of defeats the purpose of all your magic defense stuff.
The first thing I want to point out is that RUN isn't a DD. Yes, it can have some impressive spike damage with lunge, swipe, and resolution. But the cooldowns ensure that this means you can't really spam it. So how do you keep hate if you can't compete with the DD's? Well, it's pretty simple: You rack up Damage-volative enmity (CE) and then NOT TAKE DAMAGE.
Okay, that sounds weird, but with the fast cast bonus from Inspiration fully merited, you can get a 30% stoneskin cast time. That makes it very difficult for you to ever get interrupted. Throw in some Blink if you like, and Phalanx to make it last longer.
Bam, you are now holding hate. Throw out a flash and resolution now and again to keep it up whenever you do take damage, keep refresh up for MP, and you're basically untouchable. I can handle WKR and Delve NM's with very little trouble, only a few emergency heals from big attacks if I don't manage to liement or one for all them.
The way RUN is meant to be played isn't so much relying on parry or evasion to mitigate physical damage, but to keep casting your defensive spells to make yourself withstand any kind of damage, physical or non. The bonus of this is that a lot of end game major attacks are magical, so even if they bust down your stoneskin, you have a ton of magical defense as well as liement to absorb it. This makes you pretty dang powerful, and I don't even have that much -pdt on at all.
There are a few downsides to this playstyle:
-You will burn your MP fast. I found meriting my MP to be a good decision. Keeping refresh up will help a ton.
-You won't deal a ton of damage. Like, at all. While you can tank a ton of stuff you rely heavily on others to actually kill the monster for you. Lower level stuff mostly gets one shotted by lunge though.
-While you aren't as reliant on a devoted healer as a PLD might be, you do have a different kind of synergy with your allies, and choosing your teammates is a different dynamic than for a PLD. Whereas a PLD would love a WHM and a BRD, and then a potent DD like RNG or MNK, RUN just needs a good DD and maybe a sub-healer to work things over. GEO is a good ally, as are many physical jobs due to your aoe defensive buffs. BLM's are your best friend if you love to use Gambit (which can generate a ton of hate, btw).
You shouldn't really worry about doing anything other than buffing yourself and your allies, and making sure you watch for chances to nullify attacks with Valliance, Liement, or One for All. Use Lunge and Resolution whenever you can (I'm assuming Dimidiation will also be very powerful), and you'll have a hard time losing hate to anyone. Flash can be spammed as well, and is very useful for grabbing emergency hate after eating a big hit.
With the new update coming out for the new enmity spell and WS/TP buffs/changes, this will likely become even easier to hold hate. A lot of people bash on RUN for not being a 'real tank', but with the recent additions, RUN is definitely challenging PLD's place on the tank throne.