Tank Stances.

[Lyth]

It wouldn't be difficult to artificially force more defensive stance usage. But inflating the incoming damage by a flat percentage or throwing in completely random damage spikes (both of which just increase average damage) doesn't really add anything to the gameplay. You also have to remember that, even as things are now, not everyone who wants to stay out of defensive stance is able stay out of defensive stance. Content is targeted at players of many different skill levels. You will always find it difficult to stay in that sweet spot where the mitigation check is just right for your specific gear and skill level.

If you want more interesting mitigation challenges, you either need more complex damage patterns, or telegraphed damage spikes that still allow the player room to prepare. The damage spikes from Brute Force and Magicked Mark are not any more random than Living Liquid's cleaves. If there's a pattern that can be memorised, then you can design a mitigation rotation around it. The complexity doesn't prevent stance dancing. It just means that fewer players will be able to pull it off. It also may mean that fewer tanks will be able to handle the pattern even in defensive stance.

Increasing the frequency of tank busters doesn't really make the mitigation rotation more complex. It just forces more swaps. Any tankbuster interval greater than 35 seconds gives you enough time to reset Rampart between the first and third tankbuster. Anything less than 20 seconds allows you to mitigate two consecutive tankbusters with Rampart (Brawler's Single Beam can occur twice in a 14 second interval, and that's the only example that I can think of this.) Fights like Twintania and Odin were anomalies in ARR in that they give you a 30 second interval between tankbusters. But it's worth noting that the Infirmary debuff on Death Sentence was probably intended to force a swap, and we forcibly solo tanked these fights despite this.

The short-recast cooldowns (Sheltron, Inner Beast, Dark Mind) kind of throw a wrench in all this as well, because they usually give you a surplus of cooldowns. But they'd be more interesting if you were forced to use them on short notice to react to telegraphed but unscripted damage spikes. At the moment, Dark Mind is the closest thing that we have to resource-based mitigation this expansion, in that you need to decide whether the Dark Arts cost will help you stay out of stance or not. Inner Beast could achieve the same effect, so long as it doesn't get completely overshadowed by Fell Cleave. I think this could be done if they made it stance independent, lowered the stack cost, and gave it a recast. This could force you to stay above certain resource thresholds in order to fend off damage spikes.

The problem isn't in players' stance usage. It's in finding a difficulty level for tanking content that is equally engaging across different skill levels.