I would lean toward no on this. Or, at least, not necessarily. There are undoubtedly many conditions we set upon several species that cause individuals unsuited to live in our lifestyle to die, but the thing is our lifestyle is such a rapidly changing thing that it is difficult to pinpoint a particular trait that is best suited to survive an era. Take the classic case of the peppered moth. I'm sure you're familiar with it - (in a nutshell) the dark coloured moths, who, at first, were the least dominant type, began to outnumber the lighter ones as a result of the darkening of tree bark in the wake of the industrial revolution. Fast forward to today, and we're very much heading toward cleaner energy which would lead me to believe that the lighter ones may once again become the more dominant in numbers.
I suppose what I'm trying to say is that I disagree with the implication that the surviving individuals have to be stronger. They're simply more suited to whatever condition we expose them to at that particular time. Does that make them better suited (or prepared or stronger) for what ever nature has intended for them (e.g. next mass extinction?)? I would say... not necessarily. But it is interesting to think about. Certainly there are cases where that may end up being true.
To be honest, I haven't thought much on the topic before so any feedback would be great.
Edited for accuracy.
