Meh. As long as the lithium battery is as easy to replace as it was to perform other Steam Controller repairs, it shouldn't be a big deal.
Think about how many AA batteries will end up in a landfill over the lifetime of the controller VS the typical lifetime of the lithium battery. The AA batteries lose every time.
Think of it like this: You can replace the battery once every two years (if the controller lasts that long in your sweaty ass hands 🤣) or you can replace the batteries every month... 24 times, adding 48-96 batteries to the landfill in that time.
To be fair, "avoid change at all costs!" Has been the Republican motto for a long time now. It's right up there with, "ignore reality."