Is a toy engine necessary for the leaderboard?

The toy engine run at the same speed as steam engine. The only differences are that there's no limit to the number of resets and the maximum number of freight cars they can connect to is smaller. Therefore, I don't think they're very relevant to speedrunning.

What do you think about removing the Toy engine category?

Unrailed! has the Endless Kids category, but most players don't play it. The toy engine category is similar in that it's a alternative to other category, but it doesn't have much competitive interest.