Definitely a good point there. However I should point out that even though in some cases where MVenu is "outclassed", he excels in other areas that Amoonguss cannot.
MVenu isn't primarily a tank. He's designed to have respectable damage and be naturally bulky due to type and ability. His form of pressure is his ability to do both. Amoonguss' main strength is support through the use of redirection and sleep, and he does this by just being tanky. Against certain compositions where MVenu excels in, Amoonguss' best option is supporting his team while tanking hits. MVenu can handle certain threats better and be a huge threat against certain teams, essentially locking down many games on his own. Amoonguss on the other hand cannot apply similar pressure but instead focuses on supporting the team to deal damage. Synthesis under Sand/Rain is also a bit redundant, because under those conditions you'll be healing considerably with Giga Drain against those weather setters anyway.
On another note, for TTar, it's hard for me to say he is deserving of S rank in today's meta. His strengths are there sure, but he takes too much punishment from the most common Pokes. Nearly more than half of the common Pokes have a SE attack against him, and even though he is reasonably bulky, being 2HKO'd is still not something to boast. He sits at a reasonably low speed tier meaning he's prone to common WoW users (even standard special variants are hurt hard from burn due to the residual damage of Burn + LO) as well as needing to tank most of these SE hits before he even moves. That being said though, against certain Pokes (i.e. ones that don't have a SE attack) he does his job respectably well, walling Salalmence, Hydreigon, Talonflame, Gengar, Pyroar, MManec, and Rotom-H with little issue. But against the rest of the meta he has some huge issues tanking. I would have to say A rank due to this glaring weakness to common attacks, but he does have his strengths being a thorn to a good amount of special attackers.
