Hi MB2002,
what would happen if an AP in a 737 had ...... the pitch (coupled) with the ASI to maintain airspeed?
Respectfully, doesn't it depends on the particular flight regime? With fixed power set e.g. During Climb & Descent the autopilot controls speed with pitch.
Also in a visual circuit whilst descending or when hand flying a NPA - pitch controls speed, and power ROD. When there is a profile to fly e.g. ALT, VS, FPA, GS etc. then it's reversed.