Do you think spells can be just as powerful as evocation?
Well… yes. But that’s kind of a “comparing apples to oranges” situation. Unless you mean invocation (opening yourself to internalising the energy and qualities of the entity) as opposed to evocation (calling the entity to appear before you, separate and external)?
Or do you mean more along the lines of candle magic / honey jars / poppets / witches’ knots vs. petitioning an entity?
Someone more experienced can probably weigh in here but I’m inclined to say neither is necessarily more powerful than the other; it comes down to the strength of your intent, how much energy you raise and direct toward the working, how well you let go of lust for results, et cetera.
It depends on what kind of spell you do and why. Remember that when you’re doing spells it’s your energy body carrying out your intention. When you call on a spirit they’re carrying it out.
So it’s up to you whether you want to put that trust into an entity that is probably more powerful when it comes to manifesting (just due to the fact that they’re divine, not saying your magick can’t be powerful) or whether you’d prefer to trust yourself.