Board Thread:Questions and Answers/@comment-27327020-20160404174206/@comment-13682699-20170411004932

It doesn't matter if the souls have influence over the being who possesses them. Flowey with 6 souls is still stronger than everyone regardless, except for a being who possesses 7 souls.

If you are referring to Flowey/Asriel, then no, their ATK and DEF are from possessing practically limitless power. If your are referring to Frisk/Chara as a collective being, then you are still wrong because ATK and DEF are core parts of the Undertale universe. They would still exist even if Chara were to never exist at all. Chara says that they embody the characters POWER and DETERMINATION to gain even more power. ATK, DEF, HP, LV, and EXP are all part of the characters overall POWER over others.