Why the United States built forty-one early ballistic-missile submarines

Was procuring all forty-one 'For Freedom' SSBNs a mistake because the Ohio class later replaced them?

No; the large early fleet supplied the hull numbers needed for continuous deterrent patrols until better submarines could replace it.

The panel explains fleet size through availability rather than headline inventory. One unique ship demonstrates a capability, while several hulls are required before a navy can promise that one will reliably be on station through training, maintenance, and refit cycles. Forty-one boats could sustain roughly ten patrols while other submarines worked up or underwent deep maintenance. The United States accepted that later boats would be better because it needed a credible sea-based deterrent immediately. This makes the program a case study in buying sufficient numbers now rather than waiting for a technically superior but smaller future fleet.