But this is discussion feedback so what in your opinion is special in the combos you mentioned?
Or what make them special in comparsion.
I will just talk about the basic mechanics of the classes, excluding all utility, support, CC, aoe, debuffs, ISS, etc. Just so that nobody cries bcz I missed 90% of stuff.
1. Wl/S casts shot with every hit of Severed Consciousness and Dark Rain. Your SC deals the most dps of all your spells, so you wanna channel this like 100% of time. To reach this, you need to manage your psi recovery properly through several sources, such as your Saces Impatience. But this only works while your willpower buff is running, so out of it you wanna use Dark Rain in combination with a tic of Knowledge Acquisition and a single shot (if other sources are on cd) to get 6 psi as fast as possible. Not to lose too much damage, you need high focus for your Dark Rain as well. I've seen many Wl/S who dealt good damage but only a few that took the entire potential of the class, which requires more than a simple spam of SC.
2. Wl/Ch casts Severed Consciousness too, but only in the offburst for sustain dps and uses Ruthless Judgement in burst with a high cast speed. You have several fillers that cost rage but at the same time you need as much rage as possible anytime to cast Rage Sublimation if you need it. You also wanna keep Saces Impulse running, which gives you a decent selfheal and additional offensive attributes. Other than Wl/S your base magical damage is pretty high, so your aoe spells deal more damage normally.
3. Wl/R has one of the most complex rotations, because you need several conditions for your best spells. You need as many elemental weakness debuffs on your target in order to deal the most damage with your strong abilities. Basically you buff yourself with Shadow Step, Punishment (that requires Crime) and End of Thoughts (that gives you the psi recovery you need). You also debuff enemies with Soul Fang (which is overwritten by Wl/M support, which you need to have in mind). So different to the other warlocks, you don't spam or channel the same spell over and over again, but rotate through a lot of different spells that buff or debuff for short durations but are essentially for your dps.
4. Wl/W uses Consistant Heart Strike as main damage source, which is your main spamable. Since Wl/W is one of the easier warlocks, you deal like 80-90% of your damage just with that. However, you need to keep up your debuffs so your rage does not run off, but since last patches this shouldn't be an issue anymore I guess.
5. I could even talk about Wl/M, which has a really funny mechanic as well: You cast your strongest spell Flaming Heart Strike which goes on cd for 20 seconds. So you cast Soul Brand String to reset the cd, but it only works in your willpower blade. The basic rota is using both skills over and over again, while keeping up the raid support and debuffs etc. You can actually deal good damage with this, but not as much as other warlocks ofc, since Wl/M is a main support class.
Conclusion:
So basically you're right: warlocks deal damage inside the willpower blade and wanna enter this state as soon as possible, in order to keep up the damage of their best spells in the first place. BUT depending on your sec class you have different ways and options to manage psi and maintain your willpower blade or you got an entirely different rotation of skills or even an entirely different set of skills.
This being said, in terms of balancing they are more or less equal as well (except Wl/M which is a meme class as dps), depending on raid setup (Wl/R requires a M/Wl imo for example for it's full potential), but not in every situation or instance. If you play warlock, you should play them all, in order to have the best options for different use cases.
Ofc you can just spam Psychic Arrows with all of them, but this will result in really sad damage. Warlocks are the most complex classes for magicals (imho), they got the very most conditions for their spells but got a lot of support and utility for the entire raid on the other hand. If you say warlocks are all the same, have a look at mage class before, since warlocks are way more diverse in gameplay than mages (and many other classes as well). 
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