Nope, nope and nope.
1. Chou Shinra Tensei is a widespread attack, thus the smaller the target, the less damage taken by the target, and vice versa. Easily explained by pressure, and the experiment where people lay on a bed of nails, but they don't get punctured, but if you were to lay on one nail, it'd obviously pierce your body. The bed has more surface area than the single nail, so despite the fact that a bed of nails>>>>>1 nail, the latter will pierce. Once again, same concept here. Due to the widespread qualities of the jutsu, and the fact that Katsuyu (at the time) was human sized, tanking it is not a feat.
2. Everything at the epicenter was obliterated without a trace, farther outwards, people survived, some with Katsuyu, some with no protection. (Tsunade and Fodder Anbu) Unless you want to admit that Fodder Anbu=Tsunade=Mini Katsuyu when it comes to durability, then there is no feat here to talk about, at least, not one that'd let her tank Hirudora, which is weaker than CST, but not as widespread.
3. DB being specific about physical attacks doesn't change the fact that using blatant hyperbole as evidence isn't gonna fly. No logical hype or feat puts Katsuyu in the same tier of durability as V3 Susanoo, aside from the ridiculous hype of it tanking all physical attacks.
4. Kyuubi Naruto's Corrosive Chakra's best feat is burning up Orochimaru's snakes. Ribcage Susanoo>>>>>>Orochimaru's Snakes when it comes to durability. Using that as evidence for Katsuyu tanking something that raped a V3 isn't gonna help your case.
You have tanking Shinra Tensei and tanking Corrosive Chakra as a feat, but the former didn't even kill Anbu w/ no protection, and the latter's best feat is burning up some generic snakes. How is Katsuyu more durable than v3 Susanoo again?
Lol