Is a pH-neutral shampoo always the gentlest option?

Not necessarily. pH describes acidity or alkalinity, but a product's effect also depends on its surfactants, solvents, concentration and additives. A pH-neutral shampoo is generally the safest default for protected paint, yet a poorly formulated neutral product can still leave residue, while a mildly alkaline pre-wash used correctly may be appropriate for heavy dirt. Follow dilution instructions and choose chemistry based on the contamination.