This is something that's always going to be contentious, and was something we debated heavily internally. When we assess the pros and cons of a system like this it's important to look at what happens when it goes wrong, what are the worst case scenarios.
Escape: You dash a very tiny distance and get wrecked, when you meant to go far. This is also done in a panic scenario when you _need_ to be as frame fast as possible.
Engage: If you dash a short distance your entire approach fails. In this scenario usually when engaging you have more preparation time to aim the spell the full distance, but it's still a painful experience.
Jungle: If you dash _futher_ than you want in the jungle it can be frustrating, and in the worst case you can mess up your route by going over a wall. However, jungle clearing is lower stress and time dependant. Additionally the worst case scenarios tend to only happen once as you can pretty easily adjust your positioning to avoid the problem. I don't view the jungle cost here as substantial at all. And if we were to adjust the distance to be short - say in the presence of a jungle monster, it would 100% cause a lot of ruined escapes by accident.
Lane Engages: This is def more mixed, but the use cases frankly are difficult to predict or intepret. Often you want to go far and intentionally reposition through an opponent, sometimes you don't. There's no universally better outcome in this type of pattern imo.
Overall - It's also critical that the behavior is consistent so the player can learn what to expect both as Tryn - but also with other champions with similar abilities. So combined with all the breakdowns above it felt like a pretty straightforward call to do the long cast version as the default. We did experiment with both versions, and the feedback was overwhelming negative on the short cast versions, though it did provide better results in the specific scenarios you mentioned.