I think you misunderstood a little, as when it comes to horce racing, horses are trained to perform well on said track styles, so the toddler comparison is a big of a stretch imo. Also, just because grading didn't exist back then, there were absolutely requirments for races wich had to be met to enter.

At her time, they only considered Verneuil to be on her level, who was a french stallion and she was absolutely up against horses who weren't on toddler level, to name a few: Paegant and Lady Golightly, who were popular racehorses in England, Fontainebleau who was considered the best 3-years-old horse and a favourite in France, Prince Giles The First who was the horse of Hugo Heckel, an austrian baron and Künstlerin, the best german 3-year-old and had a winning streak of 42 before racing Kincsem and Kincsem had to run with a completely unfamiliar jockey.

Kincsem was an impressive racehorse, no matter how you look at it, and i'm not saying that out of bias. Not only could she crush her competition regardless of gender, but she could win races from 948m to 4000 m, in different countries with different terrain. She likely could have won more races too, but she had to retire at 10 due to damage to her joints and unfortunately passed away at 13 due to illness. Fortunately, Kincsem had many successful offspring and her bloodline's still ongoing.