Why are there extremely slow spells?

Why are there EXTREMELY slow projectile speed spells like ball lightning, essence drain and frostbolt in a game where you 1 shot the entire screen immediately with 80% of builds?

The same reason 96% of melee skills are worthless.

Ball lightning is slow so that it can hit targets more before they are out of range, frost bolt is slow (i assume) so that it is easier to target for vortex, and ED i prpbably slow so it gives you time to contagion everything?

so you can bypass it with cast while channeling

You can make projectiles faster.
Ball lightning is a spell you want slow, so it can zap more enemies.
Essence drain is great in combination with contagion. With a slow essence drain you can shoot the projectile and then cast contagion - granted, this would also work OK with a faster essence drain.
Frost Bolt is really hard to rip apart with vortex when the balls are too fast. If you want fast frost bolts and don't want to use vortex, you can always add projectile speed.

Moreover, strange as it may sound, some people prefer a play style other than "press button - watch screen explode - proceed".

Man, I even use slower projectiles on all the spells you listed. My question to you is, why not?

Some spells are more effective when moving fast, some are more effective when moving slow. Depends on the mechanics of the skill. What's wrong with that? Understanding when amd why it is better for a certain projectile to move faster or slower is the job of the player, by design.

I'm not sure if I worded my question correctly.
I'm trying to say that:
If you can go a spell/attack that has NO TRAVEL TIME or nearly none and kills the entire screen, why are there spells that move extremely slow?

Why would you ever go slow projectile attacks if fast ones offer much faster clear speed?

This video kind of demonstrates my point I'm trying to make. He goes a DOT build and uses a DOT gem link that offers 0% up front damage and still 1 shots mob packs. Him casting the projectile that's meant to be used in conjunction with vortex(frostbolt) is a clear speed loss. Why would this work this way?
https://www.youtube.com/watch?v=mrAqeSv2IeA

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ShiyoKozuki написал:

I'm not sure if I worded my question correctly.
I'm trying to say that:
If you can go a spell/attack that has NO TRAVEL TIME or nearly none and kills the entire screen, why are there spells that move extremely slow?

Why would you ever go slow projectile attacks if fast ones offer much faster clear speed?

This video kind of demonstrates my point I'm trying to make. He goes a DOT build and uses a DOT gem link that offers 0% up front damage and still 1 shots mob packs. Him casting the projectile that's meant to be used in conjunction with vortex(frostbolt) is a clear speed loss. Why would this work this way?
https://www.youtube.com/watch?v=mrAqeSv2IeA

Cause different tastes,for different people.Not everyone wants the same pace.Not everyone uses the same skills.And also because each skill can serve different purposes,like the ball lighting for example,not better knockbacking skill in game

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ShiyoKozuki написал:

I'm not sure if I worded my question correctly.
I'm trying to say that:
If you can go a spell/attack that has NO TRAVEL TIME or nearly none and kills the entire screen, why are there spells that move extremely slow?

Well... Really, the short answer is:

Game used to be balanced around enemies actually resisting death. So slow spells weren't really a detriment because no matter what you weren't going to be wiping a screen with the blink of an eye.

However, damage has since scaled to the point where you will just mass nuke everything in 0.001 seconds.

Now, slow spells are pretty much just relegated to leveling and utility (Leveling with Frostbolt + Ice Nova/Vortex can be effective. Meanwhile, Ball Lightning is a very effective target for Curse on Hit, especially for multi-curse set ups due to the large volume of hits it will do with a single cast)

Of course, Essence Drain is there for those players who want to use pure Chaos Damage. Since it's one of only 3 Chaos Damage spells. It's also the one that deals the most damage (Unless you can maintain really high stacks of Blight)

Essentially, they are fine skills that are left behind because of the speed meta caused by power creep.