Sorry but let me contradict you.
1,730 species were discovered in 2016, so what? This does not mean that those species were born in that year.
They probably already existed for thousands, if not millions, of years!
The 571 extinct species, on the other hand, will never come back.
This means that overall there has been a loss of plant species, not a gain.
If you want to bring data about the species born in that year then we can discuss it, but good luck whit that, because when you discover a new plant species it is very difficult to determine when it was born and consequently the data in this regard are very vague.
Since one can not prove a negative, your claim is not falsifiable and therefore unscientific. In order for a particular claim to be scientific, it needs to include the conditions under which that claim would be rendered incorrect.
Therefore, the claim that few of the 1,730 species are new rather than simply newly discovered has the same scientific weight as the claim presented that plant species are dying at the rate of about 2 or 3 per year.
It's important to note that plants evolve quickly. In fact, farming has modified plants genetically over the last few hundred years. And I don't mean the supposed GMO products. So, it's quite plausible that at least 2 or 3 new species of plant life have appeared on planet Earth over the last 250 years or so.
What we do know and can measure, is that the Earth is significantly greener than 50 years ago. Within all that new green plant life, it's quite likely that new and simultaneously undiscovered species are now thriving.
See, the point is that even your claim that new and undiscovered species are thriving is not scientific.
There is no scientific evidence in favor of this statement, therefore the whole discussion is based on conjectures and opinions.
As far as I'm concerned, knowing that the extinction of plant species goes on so fast worries me.
Actually, there is a way out of the conundrum...
The appropriate question is:
What is the rate of genetic change in plant life?
This question is still a bit broad for an answer, so one should ask:
What is the rate of genetic change in grasses or small short lived shrubs?
The answer should have the form of: Y new species per X generations and then we could have a discussion about something scientific as well as answer the question of extinct species versus new species.
Yep, that's the question.
Sadly I don't think we have an answer yet.