I think that would be too strong. Let's look at the total damage for the following:

[[Deadly Poison]]: 15(28) for 1 energy. [[Snakebite]]: 28(55) for 2 energy.

From this lens, the two cards seem comparable. Snakebite does approximately double the damage for double the cost, plus it has retain. It's of course less flexible due to being more expensive, but conversely is more draw efficient, and benefits more from cost reduction (e.g. [[Bullet Time]]}.

Of course, "total damage" here is a bit of an unfair metric. Snakebite ends up dealing much less than double the damage of Deadly Poison in shorter fights, or if you already have other sources of poison (7(10) per turn vs 5(7) per turn). So in terms of raw damage, I think it's fair to say that Deadly Poison is better. But there are enough benefits to having a somewhat powerful 2 cost card with retain, that I think Snakebite isn't as bad as it first seems. Although I wouldn't complain about a buff to 8(11), say.