Poison implies something that slowly devours you and your body with little ability to control/quell it. I see ambition as inherently good. It's the "constant pursuit of perfection".
This "poison" is easy to deal with - just go again next year and win it.
At what cost, though? From DHH's post:
When you expect to win, it’s merely a checked box if you do — after the initial rush of glory dies down.
Winning isn't everything, and in fact can mean very little. Spending exorbitant sums of money (LMP2 isn't cheap) and risking your life (not everyone who started Le Mans on Saturday lived to finish) might not be worth it.
You are supporting the author's point.
Ambition is simply a tool for achieving goals, thus it cannot be inherently good or bad. It is the worthiness and nature of the goals which define whether a particular tool is good or bad. For example, I would argue the "constant pursuit of perfection" in child-rearing is bad approximately always.