Keep in mind that I'm coming at this from the PoV of someone using an xbox controller, letting me hit 7 abilities out of 8 abilities with my Right thumb so I'm not even as bad as it could be if I was using a PS controller or keyboard.
TL;DR is that Twinblood and Twinfang should be consolidated into Serpent's Tail.
Viper right now has the least number of buttons out of any job, but the way the job is designed forces you into very restrictive button layouts or risk bloating your hotbar with multiple duplicate abilities.
Controller:
I'll give an example, in order to comfortably execute the Dreadwinder combo, you need 5 buttons, so say you have Dreadwinder on your D-pad in a position that you can hit with your index finger while piloting the analog stick or reach comfortably reach with your thumb, and then assign your 4 other buttons to face buttons in way that you can comfortably hit them in a clockwise or counterclockwise movement.
Then you come to the realization that you need Serpent's Tail and not Twinfang/Twinblood in order to perform your reawakening combo so this button layout doesn't work anymore.
In order to actually make your crosshotbar efficient while also allowing you to simultaneously use your analog stick and face buttons, you need your abilities on a different crossbar than your weaponskills so that you can access them from any of your weaponskills, which then opens up a can of worms as you're constantly pressing and releasing your trigger buttons to do ogcds which quickly causes more hand fatigue than other jobs.
Keyboard:
There's no way around it, Serpent's tail has to be bound to C and then the other two dance around it. Anything else and your thumb has to extend outside of a comfortable range to constantly hit your abilities. This is really annoying because it means you also need to reserve V and Spacebar for your other two if you want to avoid overtaxing your thumb.
Ironically, Viper is really, really easy to click through. You need to duplicate Serpent's tail 4 times, but you can basically draw a T block with your ST skills on one side and AoE skills on the other. Position your Serpent's tails in-between your Dreadwinder positionals so that you can basically draw zigzags for reawakening and then surround your Twinfang/Twinblood buttons with their combo skills. It's super comfy to go through and you can bind your utility abilities on easy to reach buttons if you need to.
Solution
Consolidate damaging ogcds into two skills at most, but optimally just 1. Being able consolidate them into 1 might be an oversimplification, but this allows you to feasibly do the a dreadwinder combo with just face buttons. At the very least, Serpent's tail needs to be consolidated with one of the Twin abilities so that Reawakening isn't a pain to plan around.
Edit: I was wrong about the oversimplification and I'm just gonna leave this up otherwise the replies wouldn't make sense. What I should have asked for is are the Twinfang/Twinblood also turning into Legacy ogcds which accomplishes the same goal.