“quality”=“gets me the answer I’m looking for, if it exists, and as quickly as possible”. Regardless of whether I was making a simple nav query or trying to figure out what an error message from some obscure piece of obsolete software really means. No other metrics need apply.
Unfortunately, Google still has the largest database of pages indexed, even if its frontend sucks like an industrial shopvac. So it can sometimes answer questions that engines using other databases as backing can’t, even if locating that answer is like fighting back a horde of zombies with a paring knife.