Not that long ago, Tsuraoka mentioned some kind of antibodies that caused certain talented to be resistant to transformation into monsters was the primary theory for how to solve the monster transformation, specifically those who's talents were "powerful" but couldn't identify where the line was drawn. This is by no means confirmed to be the in universe answer nor do we have any idea what the theory is based on, so while these could be red herrings, let's take some time to see what this would have to mean if Tsuraoka does turn out to be correct in his statement. That would mean there is a group of talented individuals who possess these antibodies, an objective and binary classification, who are also powerful, a generally subjective and relative term. That would require some sort of objective way to confirm who is powerful, as without antibodies they are no longer in this group. He then gives a list of either talents or talented individuals he suspects qualify as antibody candidates, who are:

1. Nanao Nakajima (Nullification)
2. Jin Tachibana/Rin Onodera (Shapeshifting)
3. Kyoya Onodera (Immortality)
4. Sachiko Maezono (Teleportation)

A quick word on Kyoya

The first two are who he has currently as test subjects, while the other two are people within Nana's faction who he would like to have volunteer for testing as well. Kyoya Onodera is especially noteworthy, as they had likely already used him as a test subject at this point in time, as he was captured by Tsuraoka along with Rin before the time skip and we see him later as leader of the watchers, so they must have had the opportunity to run experiments, so why make him a watcher? I suspect they likely did run experiments on him, likely multiple at a time without breaks, as he does not require recovery time. They likely had gotten all of the data they needed from him that they could at the time. Then, in order to convert him into a strategic ally, one who would willingly submit to voluntary testing again should the need arise, they went ahead and mad him a watcher, not just to win him over with a privileged position in society, but to give him the time needed to forget about the excruciating pain he was just put through. Had Nana not managed to reunite him and his notes thanks to Fuuko Sorano, Kyoya would have likely submitted willingly to his perceived allies' request, which could have been any level of torture they deemed necessary. However we'll get more into Kyoya and his talent later, so much more into it.

Who else?

While these four all are incredibly powerful with talents that would be envious of, and from amongst the remaining casts are certainly the talents more relevant in reference to the current story, there are others who are just as powerful, such as Shizuka Saeki, who uses her talent to effectively resurrect then entire population of escaping talented and their families with her time travel. She was still alive at this point, and while sure that had not happened yet, Tsuraoka should have been aware of her power, so can we truly say these are the most powerful?

The Obvious Candidates

Within not just Tsuraoka's list but the cast as a whole, the two most universally agreed upon powerful talents are Kyoya's immortality and Rin's shapeshifting, specifically when shapeshifting into other talented people and using their talents herself. You do not even need to read the series to understand how powerful these are. Immortality is probably the single thing that the most people throughout human history have spent their time trying to figure out a way to make possible, whether for themselves or loved ones (or their king, and the ability to shapeshift into an immortal and also have his immortal with the only requirement he's still alive is, well, also just immortality with sprinkles on top.

If I were to ask you to make a list of the top 5 best talents, both of these would be on almost everyone's list. These are so far and above the average power level of the series that only a handful of other talents can even be compared to them, and they are shared by the single pair of characters remaining in the story who are confirmed to be blood relatives. This had me thinking maybe there was some truth to Tsuraoka's belief in their being some objective difference between regular talents and powerful talents.

Not Enough Data

Having a talent vs not having a talent are considered to be likely genetic, even though the specific talents aren't, but maybe the strength of a talent was genetic? Unfortunately we have no other confirmed families with multiple living members who have talents (that appear in the story at least), so there's really no other way to look into genetics, so I started looking into something else that could be related