Percentage are broken in many cases because they are ambiguous, and often difficult to compose. +50% then -50% is not identity but ratio 3/4.

A plain explicit ratio is sometimes better. Ratio in decibel, or "doubling number" can sometimes be valuable alternative, could be used more often.

+1 doubling -1 doubling is identity. Same for decibels.

In case it's missing, I think parent's tongue is firmly in their cheek - point is things like '4500%' are often manipulatively rendered that way to sound massive, vs. '45x' for example, which means the same, is just as massive, but perhaps doesn't sound as crazy?