Beginner custom coffee maker here (Kalita Wave). Can you really tell a difference between burr and blade grinders in a blind testing? Considering everything else is equal (method, beans, etc...). Also, how much do you think percentage wise the grinder contributes to the end product?
Yes 100%
The grinder is the most important part outside of the coffee itself
Three pillars of coffee: the coffee beans, the grinder, and the water. Any one of the three is bad, the stool falls over. Blade grinders leave a variability of fines and boulders, yielding under- and over-extracted flavors. They don't cancel eachother out, so it just makes the cup taste muddy. A good burr grinder will leave minimal fines, and a uniform max size of grounds. Final cup should have clear flavor, and grinder is a big part of that.