I actually run a vastly different deck in league. I like to use the gyms to work out less used Figures. Before thinking about running this team I'd want a Crobat to replace Umbreon. Umbreon is by far my weakest link and Crobat accentuates the value of Poison while still being 3MP.

Gold teams would hurt a lot and Venusaur being down to 1MP would be brutal. The Tentacools aren't powerful enough until you can get them all out. Venusaur being down to 1MP ruins my safety net of being able to throw him on the goal and survive. I'd almost certainly have to save a Plate for Pokemon Switch. Plus in this gym when all the Tentacools are out you hit 110. This means I can X-Attack a Deoxys A (or Reun) and KO them with a Tentacool. Without the poison buff that no longer is possible. In league you'd need an X-Attack just to be safe when attacking Moltres/Zapdos/Ho-Oh.

Basically there's no way I'd run it unless I had a Crobat. Even then I'm a tad impatient and really like my 3MP runners (I use Mew/Shuppet in League). The 40 time for the gym is semi-okay for me since all my games end up taking forever just because of how Poison teams operate.