>>Perhaps each new row increases the array instead of increasing by a larger amount to create a buffer and pruning excess rows (once) at the end of the command duration - StringBuffer/Builder AFAIR increase 50% of previous buffer size, which could lead to memory trouble when increasing large arrays

Could well be. My explanation was that Copy TO ARRAY is an antique command dating back to times when we were blessed with 26 aliases and realistic memory limits measured in tens of MB. It had to be efficient with small resultsets since nobody would be so foolish as to mount huge memory-resident collections- at least not until NET and its memory-resident datasets