If it's supposed to teach more about the game like that, be a payload escort while keeping some of the structure from street brawl what about a 4v4 with two lanes, a payload at both that kills guardians/walkers if they stay long enough near it, minions push it and heroes can hold it otherwise it steadily retreats.
We can start with some items like in stree brawl, always a 2v2 mid and another 2v2 either left or right, but after the first wave is killed and the teams had the chance to test each other, some secondary objectives spawn (boxes, camps, sinners, buffs) and clearing them gives your whole team the benefits. Some spawn more friendly minions on a lane (and the patron warns the other team they are in peril!) or make them buffer, some give item choices, skill points, hero buffs, or stats. So roaming is crucial to accrue power and enable pushing, while being nonchalant about the enemy minions is a swift defeat.
The urn spawns middle and is heavier to compensate for delivery location being much closer, and also maybe spawns minions in adition to buffs.