Not trying to argue with you, but I can only repeat my experience and that of the collective Leaf Forum's wisdom. Whatever the older Leafs have their charge program set for the 12v batteries, it seems to prematurely wear the batteries that came with the car (regular lead-acid). Untold numbers of other folks on that forum who have replaced them with AGMs have not had any more issues of premature battery wear. This is not a scientific, control group study.. but the result is the result.FYI, an agm battery is a lead acid battery but with woven fiberglass inside to reduce stratification that you get in liquid lead acid batteries. Since the kwh charge rate is lower for an agm than a regular battery your comment that the hv converter kills a regular battery but wouldn't harm an agm battery simply isn't correct. If the hv battery maintainer kills any 12v battery in your car, take it to the dealer.
With that said.. I have no idea if the EV6 will do the same or be perfectly fine? I imagine the evolution of the tech and real world feedback has smoothed out the issues the early Leafs had with 12v battery charging. Fingers crossed!