True, but scorching Ray is not available to every warlock, and you have to hit with every ray for the damage to average out to more than the initial attack. Also, once Witch bolt is a DOT where scorching Ray is not. It can potentially do more damage. So in truth, it's not a weaker spell. Maybe not a spell for your play style, but if you're going to compare it, you should at least compare the spell as a whole and not just part of it.
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Its not really a DOT. It takes up your own action, and concentration, and you have to be within 30 ft. You know what being in 30 ft means? Anyone can walk up to you AND attack you in 1 turn. Meanwhile, I can stay at a comfortable 120 ft and fire EBs. If any enemy starts moving in my general direction, they need about 3 turns to reach me.
You're forced constantly use your action to activate the 1d12. The moment you do something else, it ends. You break concentration, it ends. Target walks out of range, it ends. Its terrible because it ends too easily, and even if it does not, its nothing great. It doesn't scale, and it still sucks compared to doing EB+Hex every round. The moment you can fire 2 EB bolts, it outclasses Witchbolt in terms of DPR by a huge margin.
Sure, its free 1d12 DPR once it hits. But if your group is at least competent, they would focus fire the target and it would go down in 2 turns max. And your free DPR ends there. But my Hex does not.