Fire Punch is there because the set needs it. The move of choice is Outrage. Dragonite will live 1 hit upon entry and another after the first Outrage. Venusaur will have to faint after the 2nd outrage, otherwise every non-fairy that comes in is going to get some serious damage.
When creating a counter I thought of a Venusaur with 10 moves. It can't possibly have all of the following: Giga Drain, Sludge Bomb, Synthesis, Leech Seed, Earthquake, HP fire, Sleep Powder, Roar, Knock Off, Rest
The bold ones are the ones I regarded as more common. The definite ones are Giga Drain and Sludge Bomb.
Having both Sleep Powder and Leech Seed can work for 1 pokemon. Then it's left with 3 moves.
Synthesis is an option that rivals Leech Seed but is the most probable. Therefore lets put a 75% that the 3rd move is Synthesis. Then we have 7 moves competing for 4th place. Most probable ones are HP fire, Leech Seed and EQ. Then Sleep Powder, Knock Off and Roar. Last, mostly unused but still an option: Rest
Having both Leech Seed and Sleep Powder is counter-productive imo, because Venu has to rely too much on RNG and can't really survive if one pokemon is already asleep. + the chance of Sleep Powder being on the 4th slot when Leech seed is in the 3rd, and the chance of not missing still work on D-nite's favor.
The EVs used on the simulator/calculator for Venusaur were: 248HP, 180Def, 252SpA, 96Spe (to cover all cases)