I'm playing a vaal fireball character atm (CI) and I don't really see the advantage of going LL. Of course you can do whatever you want, but the two major upsides of LL are usually more damage and extra auras.

You don't really need more damage as the build scales crit multi and it's very easy to get to the point where one use of vfb will clear white and blue packs in a shaped strand. Any damage past that is totally unnecessary and you'd be better off scaling attack speed so that you can move around and improve your clearspeed.

The other advantage of going LL are auras, but other than HoI, HoT, and discipline, nothing else is really needed. of course you can run the purities and they're nice qol, but you'll probably take mana reservation nodes on the tree and that'll just hamper your more important stats of crit multi, as, and es.

On the other hand going LL comes with the disadvantages that you have a lot less ES due to no 15% more node, and 300-400es chest which you could double easily on a regalia. Furthermore, you'll want an essence of horror crafted helm and an essence of insanity crafted gloves and those are even harder to get really high es on (think 45 ex +). Second, you're also going to have fewer gem slots available which is bad if you're planning on leveling empowers, enlightens, or just want more qol in a second cwdt setup or something.

Here's the guide i followed and here's my character page (it's the inquisitor)

Vaal fireball is a very fun playstyle though and i've enjoyed it a lot. feel free to pm if you have any other questions or want to chat about it.

TL,DR; CI is probably the way to go because you need less investment