You're absolutely right. The impact is different, and you could argue that the distortions are smaller in the sense that in our system, strategic voting is always at the expense of small parties to the benefit of larger parties. Under PR or MMP and so on, sometimes it goes the other way around. For instance, in Germany, if you are supportive of the Social Democrats, and you see that a potential ally, the Greens, might not meet the 5% threshold, you have voters who strategically defect towards the small party to make sure that the Greens have the 5% in order to form a coalition. You are absolutely right.
The main point is that they have at least as much strategic voting under PR, and perhaps even more. But the consequences in terms of bias against small parties are not the same.