At 5th level, I'm a wizard. I don't care too much about a single spell slot. I do care if I have to lay down a bunch of repetitive boring (since level one) cantrips spells to help take out a lieutenant. I also don't want to cast more than 1 or 2 non-cantrip spells out of my repertoire to help take down a lieutenant. I'm stingy that way.
There are several better non-cantrip spells. People are using cantrips as an example because they're ALSO better and don't even use up a slot.
Is Witch Bolt a DPR king? Nope. There are spells that do more damage.
Those spells not only do more damage but are better in every way.
The neat thing about the spell is that it is auto-damage. I can fire and forget. I don't care if the lieutenant decides to ignore the 5th level Rogue who often does 18 to 28 points of damage in a single round to focus on my wizard who is doing a paltry 6.5 points. If he does decide to do that, great. He's making a tactical error and that spreads damage around the party. I'm ok if he OAs or disengages, just in order to get away from my spell. That's either good damage or good action economy as well.
Yes, as you say, you are doing so little damage that breaking off to attack you is a tactical error.
All of the cantrips can do zero damage in a round. So can this spell in round one. But if the player makes a single D20 roll, he's in the zone with this spell. Do you know how boring it is to do NOTHING for multiple rounds in a fight, recasting the same old boring cantrips over and over and over again?
You've pretty much lost everyone here by saying running around casting different cantrips at various ranges at different targets while also keeping a second concentration spell up is somehow boring while standing there round after round using Witch Bolt on the same target and hoping it doesn't step out of range for a second or run behind an object or just die early is somehow fun.
Blah. This spell allows the wizard to contribute every single round in a fight and he does it in more than one way. Yup, the wizard is only doing 25% to 35% of the damage that the Rogue is doing. But, that's ok. It's better than doing 0% that someone who misses a lot does. The wizard does not have to be a striker.
Wizards can do plenty of damage, so what you're saying is that it's okay to take horrible spells even though better ones are available. Sure. But that is really what your argument is, that you like the spell and that is why you want to cast it, despite it being horrible.
In 4E vernacular, this is a minor control spell.
No, it isn't. Ray of Frost with it's slow effect is a minor control spell. Chill Touch with it's no heal is a minor debuff spell. Witch Bolt is a disadvantage the caster spell with the penalty of costing concentration and limiting the caster's movement! You are literally CCing yourself for the enemy.
It does damage every single round and encourages the enemy to either OA, or disengage, or ignore larger threats and attack the wizard.
Doing the LEAST amount of damage in a party DISCOURAGES enemies from attacking you. Something like Ray of Frost's slow might annoy something enough to want to deal with the wizard, but the wizard doing ineffectual damage sure won't.
At the end of this fight, sure, the wizard did a bit less damage than if he had been casting other spells. But he did it using up very few spell slots and worse case, the NPC lasted for a single extra round.
Again, could have used Ray of Frost and used NO slots AND provided some CC, *or* used Sleep or Burning Hands and been far more effective.
You don't like this spell because you focus solely on DPR.
We don't like the spell because it has bad range, uses concentration, does slow damage, ends when the target dies, ends when the target runs past an object or out of range for a second, CC's the caster by restricting their range of movement AND despite all those drawbacks which SHOULD mean the spell gets a DPR boost, it instead has bad DPR. We get it, you like the spell, keep using it. It has FAR too many drawbacks and no positives given it's bad DPR for me to load.