I had used a higher ratio in the past when I went through this thought experiment. I used five or ten species per genera, but using these estimates the number should be closer to two. Though there are more than two species in the average Genera, it would make sense that a global extinction event that took out one species would also take out a closely related species more often than an unrelated one. Still, the ratio can serve as a rough proxy for the number of genera there were in the past when you consider that such a large proportion of the worlds species and genera were eliminated that the ratio-skewing would be minimized. Its like a poll taken that questions 3/4ths of all voters. It doesn't matter much if your sample is skewed because its such a large proportion of the whole.
Now all we need is a good estimate of the number of species around today. Though the vast majority of them have not been cataloged the current best estimate of that number is 8.7 million. Some of these are deep sea animals to which we have little access. In other cases the problem is that a group of animals looks so alike that we consider them the same species but they are actually two or more species and we just haven't looked close enough to notice that yet. So let's be very conservative and reduce the number of species to those which are so different from other populations and so accessible that we already know they are a species. That would be about 1 million. So as you can see I am really trimming the numbers here as far as what macro-evolution is required to do to be validated. I am allowing for how puny our powers of observation can be.
Earth has had five mass extinctions since 543 million years ago, each about 90 million years apart. The last one was 65 million years ago so it is reasonable to assume that the others produced at least as much diversity as the last one, since they have had on average significantly more time to do so. But let's be conservative and say they also only produced 1 million new species that are different and accessible enough so that were they around today we could recognize them as such.
So there was an initial burst of animal life in the Cambrian which produced, let us say, 1 million "spottable" species. Then five mass extinctions after that which did the same. That is a total of six million "spotable" species and therefore roughly three million genera over the past 543 million years. That's the "rate" at which evolution would have to produce new genera to explain what we see. You will note that these numbers are pretty conservative given the estimated number of actual living species, that the time to produce these species is much less than the average time between mass extinctions, and even though a species may be difficult to spot a genus should be much easier to detect.
But even using these conservative numbers 543 million years / 3 million genera from "spotable" species = and average of one new genus in less than 200 years. That's how fast evolution had to work in order to produce the diversity of life we see. Is that the rate of evolution which we observe? Has there been even one case of a new genus evolving in recorded human history?
It looks from here that something else was happening in the past, a force at work which is not at work today with the same power. This fits well with the cosmology put forth in Early Genesis, the Revealed Cosmology. In it, this realm is a copy of the Land Above, but one subjected to futility. Up there, when God speaks, it happens. Down here, its a bumpy process and though creation might try, it can't do God's will without God's help. Just like us.