I would say it is too early to say the drop rate or RNG is too low or even too high. I started to fight the Dark Lord before the update continuously to get his girls. I got one in January before the update and one in February when the Valentine's Day promotion just got started. May be because of the Valentine's promotion; the chance to get the bosses' girls was put on hold and the chance to get the LOVING GIRLS was the top priority. During that period I got Loving Lupa from the Dark Lord and also Loving Bunny from the Ninja Spy. After I got Loving Lupa I got Princess Agate after I completed the Gems Kingdom quest. When I started the Ninja Village quest I battled the Ninja Spy and got Sung Tai Ki then after many fights I then got Loving Bunny. After the promotion ended I upgraded to Level 41. I continued to fight the Dark Lord to get his last girl Kimie, which I got when I defeated him for the 10th time at Level 16. Which is today. Initially I thought the drop rate was too high, but taking into consideration the Valentine's promotion I really think it is too early to say the drop rate is too low or too high.