Answering as a non-astronomer: Arecibo had two major advantages over synthetic aperture arrays. The first was the "seeing" power or total sensitivity. Because i

Answering as a non-astronomer: Arecibo had two major advantages over synthetic aperture arrays. The first was the "seeing" power or total sensitivity. Because it's a large single dish it collects far more photons than multiple smaller dishes. The receivers were also cooled with liquid helium IIRC so the noise floor was ridiculously low. Those features combined made for not just high resolution but high sensitivity observations. Most telescope arrays (to my understanding) have a higher noise floor. The second feature was the ability to transmit. Arecibo has been used for decades as a radar to image asteroids and such. Many asteroids are too small and dark to effectively image with optical telescopes where Arecibo's radar is no problem. It also gets extremely accurate distance and rotation measurements.