So far folks have mostly responded to my question (how is this one thing the same as this other thing?) with an explanation of how attribute tags can be used to differentiate them. That’s well understood, but it wasn’t the question. Attribute tags can also be used to differentiate two dissimilar things tagged highway=cycleway so this is not an argument for why leisure=track would be a more suitable top level tag (aka primary or feature tag).
There was one response stating a reason why the two things could be considered to belong under the the same top level tag:
Does anyone else have others?
Most of the sport=* values documented on the wiki are consistent with my understanding of what leisure=track represents. toboggan seems out of place to me though. Would it include Summer toboggan - Wikipedia?
Sure. We could even do away with the concept of top level tags entirely! Data consumers can figure everything out from attributes, right? Just tag everything with width, height, access, surface, smoothness, maxspeed, sport, etc. /sarcasm 