Lv. 66 WAR here. The last time I wasn't the solo tank for any exp party I've been in was my first party in Yuhtunga Jungle. My party has been able to get chains 4-5 consistently, be it against Goblin Smithies at lv. 30 or Toramas at lv. 60. We got chain 4-5 consistently against Tormentors in the Den of Rancor at 66 the last time we partied.
Can WARs tank past 60? Hell, WAR tanking is only just starting to get really good at 60.
The catch is that WAR tanks have nowhere near the independance that PLDs or NINs have. PLDs and NINs can go for long stretches with absolutely no support from the rest of the party and still do ok. WARs really can't, at least until 74. Against a typical unenfeebled IT, a WAR is going to take a ton of damage and go down fast, no matter what he tries to do.
However, mages have a ton of wonderful abilities that can make a skilled WAR an exceptional tank. The primary one is Carnage Elegy, which BRDs learn at 59. This single song is the reason why I say WAR tanking really takes off at 60. Combined with Slow, Paralyze, Flash, and Stun, a skilled WAR/NIN will take negligible damage. Even with only Utsusemi: Ichi, it becomes easy to mitigate damage to the point where you can just pull nonstop.
However, note all the requirements. You need a WAR who's skilled enough to manage Utsusemi and JA timers while also dealing enough damage to hold hate. You need mages who can consistently land multiple debuffs quickly each fight, and/or a BRD who consistently lands Carnage Elegy at the start of each fight. It doesn't sound like much, but those are steep requirements. As noted in this thread, most WARs don't tank, primarily due to the stigma against WAR tanking. As such, many really don't know how to handle tanking well, as even some high-level WARs have admitted on Alla's WAR forum. White and Black Mages who don't go out of their way to work on their enfeebling skill and gear will have a lot of difficulty landing enfeebles consistently. RDMs, while I love them, are like a box of chocolates. You never know what you're going to get. And finding any BRD at all sometimes seems harder than getting all those others combined.
In other words, WARs are capable of being excellent tanks. However, outside of a static party, like the one I level with, you're not likely to find a party coordinated well enough to work with a solo WAR tank. As such, as much as I absolutely love tanking as a WAR, I'll admit that it isn't ideal for pickup parties.
BTW, I've found the worst stretch for WAR tanking is the early 50s. Mobs start hitting really hard due to the different mob level exp calculations. Between that and the increased difficulty dealing damage to the mobs, hate control goes to hell too. However, we were also fighting Robber Crabs in Kuftal Tunnel that gave 245 exp per unchained kill after we dinged 51. Had we fought appropriate mobs, even those levels would have been ok. By the mid 50s, WARs have a good amount of Enmity from AF, excellent gear in the rest of the slots in the form of the RK Chainmail set, and Rampage. It only gets better from there.