As a rule I don’t say anything about AI decks using it, or how I face it, because the AI is so bad you can win with anything.
But when playing vs ai, it absolutely stomps anything the AI has.
As nissa you can have this out by turn 2 and then it turns into a 5 turn countdown.
The issue may not be its efficiency, but nissa’s ramp. For instance, red has a similar creature in terms of efficiency, a 5/3 for 8 which is 1.6 mana per power as opposed to 1.25. It seems worse in general, but it is more efficient with any reinforcement. But noone has a real problem with volcanic rambler, because red’s mana ramp is nonexistent and red needs to expend a lot more mana on control by burning.
Of course burn is a 1 mana per power ratio which is fantastic, but it still slows red down. Typically green gains between 1.5-2x as much mana as any other pw on a given turn.
So this coupled with her other big wonderfully statted reach creatures, which come with life leech, mean that Nissa with this is a powerhouse.
As soon as colossus drops it absolutely is game over for the AI, even a setback takes only a turn to recover from, because noone in their right mind would bother reinforcing it, so you can keep one in hand to drop later.
Anyway destruction is extremely uncommon when playing AI. Unsure why, but the AI sucks at burning and destroying your cards. Only 2 real cards in the game that destroy it anyway, blue and black, and those are underrepresented in pvp because they are too slow. So the reality is the card rolls over everything and is a gg if it drops in the first 2-3 turns.
THe reason I bring up the efficiency argument is that we have nothing else to compare it to aside from there. There are many vanilla or almost vanilla beatsticks in the game and this one is by far the best. Think about the best cards in the game, almost half are simply good because they are efficient, nothing to do with their effects, etc. This game is not MtG, where the vast majority of decks are built around card text and interactions, rather than simply a big ol beatstick. So yes in MtG doom blade means a big ol vanilla fatty is almost never a consideration. In MtG you are also only limited to 20 hp - with that a 2/1 turn 1 is so much better than a big fatty turn 6 because that turn 1 2/1 immediately puts a 10 turn counter on you.
But in this game with huge hp pools, and very limited ways to deal with opponent creatures, as long as you can clear a path for colossus he is an autoplay.
To put it another way, ask yourself “how many games have I played where I lost a creature to destruction? How many of those times was it actually a big detriment?” If I asked myself this, I’d say between 2-5% of my thousands of games played have I actually encountered destruction, rather than simply combat damage.
Similarly, ask yourself, “how many games have you won with spells and control, and how many have you won with creatures beating each other, where the most efficient creature wins?” If I asked myself that, I’d say approximately 0% of my wins came from spells (notable exception from enshrouding mist, but it simply gives your creatures 100000% more efficiency). Though the old jace drain and liliana demonic pact cheese deserve a mention, there are far quicker and better ways to win.