Okay, the Venusaur's attack isn't amazing, but it at least hits the lower relevant magic numbers, which is more than the last Venusaur ex can say. You'd probably have at least a few winnable matchups if you built the deck well. This also sets it apart from Lunala GX, the last bulky multiprize Base Set Venusaur successor, which could only hit for about 120 damage in a format where 180 would be the bare minimum.
The nice part is that Teal Mask Ogerpon ex can help you accelerate Energy while drawing more cards. I guess it also might be worth mentioning that Whimsicott from Temporal Forces provides an Ability alternative to Wally, but I doubt a Mega Venusaur ex/Teal Mask Ogerpon ex deck would have room for it.
Overall, Mega Venusaur ex isn't looking amazing at the moment, but it's something. Just like the original Energy Trans Venusaur, actually.