On the opponent's next turn, they will need to rely on luck, use up crucial trainer cards, or retreat all of which put Mega Venusaur's trainer at a strategic advantage with further potential to lock down even more opposing pokemon
To play Devil's Advocate, Chandelure isn't an extremely popular Pokemon and its Mega Evolution isn't the most memorable from Pokemon Legends: Z-A, so its relatively tame price tag makes sense
Defense is definitely a scary card, but your opponents will also have the rest of the table to worry about, so it has a better chance of going unopposed
Your opponents will probably be playing a lot of creatures, so having an answer to them is crucial
Cipher allowed you to cast a spell, then attach it to a creature that would allow you to cast the spell for free every time you hit an opponent with it
For two more mana, players can attach it to another creature as equipment