But we still don't know how big Konan's stamina is (so we don't know how big her chakra reserve is). It may be at the same level as Tsunade's, it may be lower, it may be higher, who knows? We know it is big (S-rank ninja, fought dangerous people like Obito) and this is fight between Tsunade and Konan, not Obito vs Konan or Madara vs Tsunade(and Kages). Konan wouldn't fight Tsunade the same way as she fought Obito nor Tsunade would fight Konan the same way as she fought Madara. Example: our conversation Konan vs Tsunade and jutsus we mentioned.
Point: you can't judge whether character ability is lower or higher (in this case, chakra reserves) based on one fight (Konan vs Obito) and then apply in other battle (example: Konan vs Tsunade) because it will be different.
I suppose you got my point.

And what do you exactly mean by ''because they both can not hurt each other''?