Hi, for me a singer with a small range, is a singer that don't have the passagio problem solved, then he uses only chest voice ==> 2 octaves range more or less. Instead of a singer that have the passagio solved, he use chest, mix and head voice ==> 3 octaves range or more , this is a respectable range.
In some cases singers use vocal fry (subharmonic) or whistle register to expand their low and high respectively, personally I think this is a valid resource but one that should not be abused because it would not fit well. In this cases you can see ranges of 4 octaves or more.
And for me a good singer is a singer which tunes well, is versatile, can sing softly or aggressively, which can add some vibrato or distortion if he wants and most importantly transmit feelings.
I think for good singers, having a tone I like is first and foremost the most important quality. Ability to sing powerful or emotional/soft performances I hold in high regard as well, plus consistency through the years.
Yeah, having a pleasant tone and good vocal control >>>> having 10 poorly used octaves/sounding like a dying cat XD But, in any case, in my head I consider that a wide range a + 3 and a half octaves range.