from what I’ve seen, they end up leveling just as fast or faster by killing enemy battleborn and minions as I do killing minions and building. They usually get 15+ Kills and a bunch of minions/thrall/buildables destroyed, while I’m focusing on building, wave clearing, and potentially getting a few kills. I tend to get the most assists, especially on overgrowth, due to me building yet I have never seen me outright heavily outleveling.
In Overgrowth for example, keeping that mid turret up is a full time job which distracts from pursuing kills, and I’m always keen on that, so I have to remain close so I can put it back as soon as I can. I gather mid shards, wave clear as best I can, and attempt to kill enemies that happen to enter mid (I guess I’m a territorial player lol). Yet my team who knows they don’t really need to worry that much about buildables (since I got them covered), can roam around harassing and assassinating everything around them. They can chase and secure kills without much worry, and save up shards to help them dispose of battleborn and minions/thralls in a quick and timely fashion.
A team full of people with 3x Legendary, now that is not good since nobody will be able to help out with buildables if they prioritize gear. I guess it’s a matter of roles and ability. I’m an awful killer but decent supporter/builder so I do that, while I leave the killin’ to the professionals. IF they were mediocre or bad killin’ machines then it’d be unforgivable for them to not contribute with building over gear.
Those are my thoughts.