Does higher proof mean better bourbon?

Proof tells you how much alcohol is in the bottle (in the U.S., exactly twice the ABV); nothing more. A cask-strength bourbon at 128 proof isn't inherently better than a 90-proof bourbon; it's just less diluted. Higher proof does concentrate flavor and can make a whiskey taste more intense, but "more intense" isn't the same as "better"; plenty of tasters find a high-proof pour needs water to actually show its best side, while a well-balanced 90–100 proof bourbon can taste complete on its own.

Distilleries choose a bottling proof deliberately, as part of how they want a given expression to taste; it's a recipe decision, not a corner they cut.