idk if voracious dispelling should have an equal chance to dispel as Dispel Magic considering the caster's investment is lesser. It costs you time just like dispel magic, but it doesn't cost you a spell slot.
It functions like dispel magic in every other way, so why should it differ in that regard?
Especially since the main draw of voracious dispelling is that you can AoE dispel, not just single target dispel as the other two invocations.
It does not cost a spell slot yes, welcome to warlock, a small selection of less powerful spells but indefinite use of them, that is the tradeoff.
spending 1 of 3 invocations on that level to be able to do just that, AoE dispels, is a significant investment.
Don't worry full arcane caster will still reign supreme in the matter of dispelling, due to them having access to greater dispel, wall of (greater) dispelling and disjunction.
All more powerful variants of dispel magic, warlocks do not have access to.