The translation on the last panel of "Nin Nin" is wrong.
Shino says
"成人モノだと弱いけどな" which is referring to adult manga and anime which are basically R-18. So she meant that the ninjas on the adult manga/anime are almost always weak. lol
"to adult things" phrase was not required though. Let me explain. If you usually play R-18 ninja visual novels or read R-18 ninja anime/manga (Eg - Taimanin Asagi), you would know that the ninjas are weak and are easily defeated by the enemies and then all kinds of sexual plays are inflicted on them. So the censored part of the last panel of Nin Nin is actually the picture of the female ninja undergoing those kinds of plays. In this way Shino retorted to Tsuda's comment earlier about ninjas being strong.
I hope it's clear now.
Also
成人モノ here means content targeted for adults and not in the literal sense of things