I can't really say anything about the Monferno analysis, having never used it or even seen it (maybe that's indicative of its status?) but in a similar vein, I think Seadra
needs some going over. I got permission to remove it from the NFE list a while ago and people were sceptical on whether it could work; it did, and I actually saw it used a few times to decent effect on the ladder. However, with Regenerator Alomomola now released, Seadra is seriously outclassed as a defensive tank due to the massive lack of recovery. In my opinion, that set needs to be scrapped. However, a more offensive variant could still be viable, in a sort of Piloswine-esque way. 95 / 85 offensive stats aren't bad by any means, and with eviolite, Seadra still has good physical bulk even without any defensive investment (enough to avoid OHKOs from CB Sawk, CB Braviary, Guts Swellow without hazard damage) Substitute / Disable / Hydro Pump / Ice Beam would probably be decent, although it requires testing.
Also yeah Tentacool is practically useless now that Toxic Spikes has become so much worse. It's pretty much outclassed by Wartortle. -_-