Actually, that's not how we use the lock feature. For the reason you mentioned we do not like automatic shut down with a preset timer. We give verbal cues to the kids as to when screen time ends, and when it's time to finish we can negotiate if they're about to finish something. With automatic shut down (which we tried for a while) there is no negotiation, kids get infuriated because their game is stopped often at the wrong time. They also get infuriated when the warning screen pops up and they lose their game in the process. Children of primary age have limited time management skills, struggle to fathom what 15min represents, especially when they are gaming, and they cannot function without parental guidance. Automotic shut down is not parental guidance
We then use the lock options so that kids that are so easily addicted to scrolling and social media don't have the temptation to open their phone to check it during down time. I had my 11 year old literally hover 1m around the phone impatient to check his phone , unable to do anything eslse. With the lock on, the kids can just move on, it's locked and that's it.
Whilst turning screen time to 0 obtains the same results, the lock button is a 2 click feature. To do the same with the current setup, with individual devices (now that the grouping option has also disappeared) requires parents to go through multiple clicks to turn on, then again to turn off. Repeat for each device. Wasted time. It is now clunky and unhelpful for parents who are trying to contain screen addictions.