No longer being able to port to village idol was the change to stop such abuse, charter stones were simply re-added in a modified form of their previous version because players wanted an easier way to trade with each other across great distances instead of being required to travel for a number of hours.Clemence wrote:Charstone in village, HF in the mine, free teleport between both like HF and village in legacy.
If I remember right charstones were made to stop this abuse.
However, you aren't wrong that they could be used in that manner so maybe limiting to porting from village idol only could be a possibility. Would still be possible to port from idol underground to charter above ground but requires much more investment than a hearthfire.