Every season when the jungle gets updated we already have to grind. Make the grind easier please.
Quite frankly, the game already has a sandbox mode and we already have to grind it. The jungle has undergone so many drastic changes and every season I either have to grind out routes or blatantly copy someone who has grinded out routes. Currently, I have to restart the game after every first clear attempt and waste 5+ minutes. I already have to do this because I play League as a competitive game and quite frankly I would consider it trolling if I went into a game knowing I might die on my first clear route. I know it's crazy but despite all of the jungle hate I actually don't want the other 4 strangers to have a bad game because I'm "practicing in game" or whatever it is you said to justify not including sandbox play. After Kha'zix was nerfed and the item that made him OP (spirit stone) removed from the game I spent hours trying to find a way to make him effective during his first few clears. The grind took hours. I had to do this because I wanted to keep jungling my main champion. It was incredibly frustrating and anti-fun primarily because half of the time was spent staring at load screens and another quarter was spent waiting for spawns.
When I wanted to learn Rumble I lost 3 or 4 games BADLY. I mean I got reported and bashed by my team even though I never said anything negative other than letting them know I was a new Rumble player. Finally I gave up and went into a game to practice my ult. An hour later I had maybe gotten 60 attempts in...60. Sandbox mode would have let me get those 60 ults in a quarter of the time. I've already been forced to grind the current sandbox mode and I'm still only a mediocre Rumble player. If I want to get good, I would have to waste at least another hour... or pray URF comes back soon.
Finally, people who have grinded custom games can flash over walls that I can't. I admit that I have just as many opportunities as them but if I'm in a situation where I NEED TO FLASH, I'm not going to try a move I'm not confident in for the same reason I never tried to flash-kick as Lee Sin at 150 ping. Why waste flash on something that has a sub-50% chance of succeeding? The people who've already practiced that flash by grinding it out even with the long cool-down or required remakes have an advantage over me so I already feel like I should grind it out. Actually, I may just take Riot's reasoning as an excuse to do something I would have considered trolling in the past. Every time I get stuck going bot lane or top I'll just immediately run to the large wall and try to flash over it. I mean, Riot did just say it was okay to practice this in live games. Maybe this is a jerk move since it reduces my chances at winning lane but I really don't want to experiment with flash when I'm in direct danger.
TL:DR The largely PvE early jungle currently forces players to grind anyways. Certain mechanics must be practiced many times before you can confidently use them in a game where you want to win. This is a competitive game and anyone trying to win has already had to grind out custom games. Sandbox mode would shorten this grind instead of lengthening it.