They are a low risk, high reward damage source as they are designed now. It's easy to spec into being tanky with high condition damage. This allows people to play offensively and defensively at the same time which is "ideal" but not healthy for PvP in a game. A major part of what makes PvP fun (for me at least) is having to read your opponent and situation to know when to switch between defense/offense. Being able to do both at once turns fights into a battle of attrition and puts people who are not built for offense/defense simultaneously at a instant disadvantage.
With the amount of different conditions that can be applied by a single profession it can make cleansing difficult if not impossible at some points. Not to mention it's child's play to bait out cleanses with minor condition application or blanket conditions since the sources from which to apply conditions are usually pretty varied. The sheer number of conditions that can be output by something like DrD, Mirage, FB, or Necro while being able to avoid/tank damage is staggering. You also usually can apply them in an AoE and they have little to no tell and are very hard to read.
Getting to the crux of the question, they are unhealthy because they promote a "fire and forget" gameplay style that allows for simultaneous defense/offense. Conditions should come with drawbacks just like power. Going "full condition" should require you to sacrifice some defensive capabilities OR conditions should be a slow burn effect that only partly contribute to your damage overall.
Burning is way too strong (this is coming from someone who just started playing fire weaver). You can absolutely delete someone with 6-10 stacks of burning in a second or two if they don't have a cleanse up. Not to mention you can apply them faster than a majority of people can cleanse so even if they do cleanse I'll have my burn application abilities up again before they can cleanse it again. Burn FB can also accomplish something similar. It's not like the burning stacks are built up over time, they show up in quick succession and if you let them tick more than once then RIP. For burning I would suggest a decrease in the amount of stacks that can be applied at once in proportion to an increase in the time they last. That way you can provide supplementary damage and if ignored for a long time the damage will become major but not hit all at once. The idea would be to apply a constant stream of 1-3 stacks of burning weaved in with small bursts of power damage.
There just need to be less sources of this. It's common, it's annoying, and can be easily used to cover damaging conditions. It's just not fun to play at points where you have 100% cripple up time because you can't waste a cleanse on it. It wont win someone a fight it's just not enjoyable to play against. I'll repeat this several times Taking away or reducing a players agency is not a fun game mechanic. This is why stuns are (usually) short and few and far between. Cripple/Immob isn't a stun but it still reduces the agency the player has.
This condition alone can shut down the whole profession of elementalist and is downright annoying on any other. As above, Taking away or reducing a players agency is not a fun game mechanic.. Not only does this slow you more than cripple, it slows your ability to react with skills. It's more or less an "almost stun" but usually lasts much longer and "breaking out" of it requires you to waste a cleanse you should be saving for damaging conditions. For this one I would remove the speed reduction and instead of causing all skills to go on longer cooldown only increase the cooldown of skills that are used during the chills uptime.
This is in a similar boat as burning. You shouldn't be able to stack enough confession to straight up kill someone with it especially since it targets your opponents agency. This should be a slow burn effect that racks up major damage over time if your opponent goes a long time without paying attention to it.
These are only the ones I see as major "issue" conditions, the others can be addressed by reducing the number of stacks of them that can be applied.
Only if you don't reapply them when cleansed. Conditions are essentially Damage Over Time effects, the key word being TIME. They should take time to really take effect. Being able to stack up enough conditions to kill someone in 1-2 ticks basically eliminates the time element.
I said reduce, not delete. If you build for high condition damage you should be tankier than a glass power build but not be an M1 Abrams.
Good, full condition builds in PvP is not a fun mechanic to play against. Conditions should be a tactic that contributes to you winning a fight, not the entire reason you win it.
Depression and anxiety are the worst...