Wait, so... you can just put literally everything into Speed and still do plenty of damage as well as avoid all incoming damage? Something about that strikes as me as a tad bit unbalanced. Like, what is even the point of the other two stats if Speed can literally do everything on its own?
Yes, speed is a "safer" way to deal damage, because you know 25% of your speed stat will go to defense and ATTACK. But that doesn't necessarily make it the best.
But attack is the only stat that actually gets rolled. It has a guaranteed effective rate of 50%, but if you roll anything higher, then that is when it starts to become attractive. You could theoretically deal 100% of your attack points if you had amazing luck. To balance that, it effects stamina the harshest.
Then you have defense. With the lowest effect on stamina and a guaranteed 50% effective rate, it is the best way to defend.
So it all comes down to how much risk you are willing to take.