Every player should improve from the ages of 18 to 25 to some degree but that is not the claim that we are discussing. We are discussing the rarity of players who are drafted with skating issues who develop into elite skaters
If Stone, Toffoli and O'Relly did improve at all it wasn't more than the average improvement and very likely was less as their mechanics remained awful which means that any small improvement that they may have made would not have been on par with the rest of the players who are also improving which is why they remained terrible skaters and never gained an inch on their competition in this regard. Of course they will slow as they age and lose any gains as measly as they were but this is a non sequitur as a reference to whether or not they had gained significant speed prior to losing it. The greatest remedy for poor skating id high IQ and these 3 have that in spades.
Draisaitl was always underrated as a skater due to his awkard appearance but the separation that he gains has always been there. There is no doubt that he has taken it to another level but the narrative of him ever being slow is incorrect. I always pushed back against that narrative and was vindicated with the Edge stats as even to this day many of the same people still refer to him as slow. People are just really bad at judging how fast players actually can skate.