Effective damage. Like honestly soldier has a lot of mitigating factors that limits his effective damage, such as LoS, barriers, etc. etc. Tracer has enough mobility to bypass all that.
If Tracer can get into her effective range (up close), she does a lot more burst damage, and can one clip a lot of heroes (and yes, you need to be landing headshots). Soldier's damage is a lot more predictable since he's normally at range at a known position, and therefore a lot more manageable for healers. So while Soldier can do more damage overall, Tracer can get picks more often because of her mobility and the bursty nature of her damage so her damage is more effective
Makes sense. But I presume this works only if you are playing in a coordinated comp setup? So Tracer will be less effective in solo queue random QP games?