I agree that saying "nitrates" oversimplifies the whole process. It doesn't take into account organic vs inorganic, fish load, feeding, etc., but I didn't want my post to get too stuck in the weeds (irony = this post); should the poster want additional information, it's already out there.
There certainly is a difference between zero and "zero" in our tests. As you stated, the nitrate reading is really only insurance to ensure there's "enough", if other, possibly more accepted forms of nutrients (e.g., ammonium), aren't available. I guess where we differ is the outcome of "not enough". Based on my research/experience, zero nitrates/phosphates have an impact on something in the overall system which can potentially lead to dinos as a symptom - I understand it's more nuanced than zero nutrients = dino, but the aforementioned weeds :).
It's largely accepted that elevated (above zero, not necessarily "high") nutrients (nitrates/phosphates) is a starting point for fighting dinos. Is there hard evidence of this? Honestly, I don't know. I relied on the experience of smarter people, including the article you linked, which all advised to dose nitrates if they drop to zero.
In my case, raising nitrates (phosphates were already solid) and dosing Sodium Silicate beat Amphidinium. Raising nitrates (phosphates were already solid), blacking out the tank, and running UV beat Ostreopsis.
It is purely anecdotal to say, "zero nitrates in each of these tanks eventually lead to dinos." Anecdotal still to claim raising nitrates assisted in beating the dinos. I did not, for example, test what happens to the Ostreopsis if I leave my nitrates at zero while blacking out the system and running UV. I have never had dinos take over a system while maintaining some level of nitrates/phosphates, but that's anecdotal at best. None of these experiences were controlled studies and I did not follow any scientific method to obtain my outcomes. So, in the end, it absolutely may be a coincidence. ¯\_(ツ)_/¯
@Kershaw, let us know when you scope the dinos, very curious to see what you have (it's like a really bad birthday present). The article
@Dburr1014 posted has some really good information on trying to identify dinos without a scope -- thank you for posting the link!