A drone need not sink a warship to matter

Could a small suicide drone seriously affect a warship?

Yes. Damage to radars or other mission systems could disable the ship's intended function even if the hull remained afloat.

A small drone could disable radars or other exposed sensors without sinking the ship. That possibility makes redundancy and survival after small-weapon impacts relevant to warship design. Electronic defences could prompt attackers to develop shielded drones, forcing defenders toward kinetic weapons or lasers if those become effective. Attackers could then favour greater numbers, speed, or protection, each with different costs. A renewed role for 40 mm guns is one possible response in this cycle.