While eight mana is a lot, you can cut it down to just two blue mana with the delve ability, making it much more manageable, especially earlier in a game
There's also trainer item cards like Rare Candy that allow trainers to evolve into Mega Venusaur ex from a basic Bulbasaur, for example
I see Sinkhole Surveyor as a beater that can get out of cheap removal range fast, and with some Bloomburrow bats around, the life loss is somewhat relevant
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If your deck has the right sort of synergy the Gem can outperform some of the best top end ramp cards but it is a lot narrower than them in general
The difference now is how you incorporate them into your deck, as many launch-day strategies are virtually obsolete now