Not even close. By lore, anyone Sword King level (~Ghyslaine) would be able to put up "decent" damage against him (Saint-level would only scratch him at most and would instantly heal). Even Badigadi himself said that Rudeus' attack is comparable to Emperor-rank (which is strong AF but there are at least ~9 God-level beings in the world). Remember, the Earth Cannon Rudeus used against him is the same strength as ones being fired by the Mk. I which only wounded Orsted not blow his torso away as it did with BDGD.
His immortality is a pain in the ass though but he does become way weaker when his body parts are blown far away or sealed like what Rudeus did. Nobody in the world would be able to "kill" him or anyone in his family permanently but once you're at the level of Rudeus (pretty damn high sure), just that would be annoying at best. The armor does make him shoot himself to Top 3 in the world and be nigh impossible to defeat though.
Just to clear something up: Water God swordsmen don't have tough defense per se despite the fact that they're called defensive swordsmen but they do specialize in counters. In terms of Touki (or fighting potential really), for some reason, they do tend to be weaker than their counterparts in other schools. It's been established that SG > NG >> WG Heck, Isolte, a King-ranked WG swordswoman at the time regularly loses to Saint-ranked Nina.