Why large surface ships are a poor Ukrainian priority

Would older frigates or other large ships be useful to a postwar Ukrainian navy?

Only in a limited flagship role; submarines and small attack craft fit Ukraine's sea-denial mission and resource constraints much better.

Older Oliver Hazard Perry-class frigates would consume large crews while remaining vulnerable to the Black Sea Fleet's concentrated firepower. Even after recovering coastline, Ukraine would have little reason to fund distant power projection at the expense of its army and air force. Diesel submarines and small attack craft fit the sea-denial mission, while a Type 31 could provide a limited flagship and command presence. Ship size should follow a state's missions and geography rather than prestige.