In point of fact, taking the numbers I've generated in this thread together with KingVoid's estimate of Schumacher (accepting that one at face value), we get overlapping ranges with different possibilities at #1.
Leclerc and Schumacher both have a significant range of variation in these numbers (0.060 for Schumacher, and a much larger 0.156 for Leclerc), and overlap depending on what part of the range you take. With the minimum gap from Schumacher, he is potentially behind both Leclerc and Verstappen. Even taking his maximum gap, Leclerc is still #1 if you take 2020 as a representative year for Vettel.
Hamilton also has a range for the Button comparison, since he has one season against Button that I consider unrepresentative (2011). If you throw that one out, he tightens up dramatically behind the leading three, and gaps clear of Ricciardo.
In outright pace, Alonso is clearly at the back of these six (albeit not by a huge margin, this is all within about 2 tenths of a second) by the numbers.