Perhaps it only takes 17 seconds currently for you, but with my setup it now takes 4 min, 3 sec for a scan to complete with my iMac (Retina 5K, 27-inch, 2017) with 2TB SSD internal. That’s significantly longer than it used to take. DetectX only needs 26 seconds to accomplish it’s scan and a ClamXAV QuickScan takes 1 min, 18 sec.
Not exactly sure how slowness relates to company trustworthiness, but I can certainly concur that Sophos will definitely slow anybody’s Macs and it has render my computer completely unusable a couple of times requiring a total uninstall/re-install, so I would echo your concerns about the impact of using that product. There are others that are almost that bad with regard to usability. I always recommend that users schedule or start a full disk scan by one of these classic scanners is to do so only when they don’t need to use the computer for the duration of the scan. Otherwise they will probably be frustrated by the impact. Some of the ratings include impact as a measure.
With AVAST and it’s twin APG, in addition to what you have pointed out, they have always had a much higher rate of false positive detections than any other tested. Their reputation has been built by scoring high on detection rates, which is fine if you are willing to chance it removing something critical to the operation of macOS or an application. I’ve never been willing to chance that.