Has naval development slowed because hulls last longer?

Has naval development slowed because modern hulls can remain viable for thirty years, unlike earlier battleships and battlecruisers?

Not exactly; modern ships can renew electronics, missiles, and even structure while keeping the hull, whereas older capital ships were harder to transform so deeply.

Modern warship development has not stopped merely because a hull remains on the front line for thirty years. Type 23 frigates, for example, have received major changes to electronics and missiles and substantial structural renewal. Contemporary combat value resides heavily in systems that can be replaced without building an entirely new ship. Battleships and battlecruisers tied much more of their value to armour, machinery, and enormous fixed gun systems that were harder to transform.