For a start, please clear up in your own mind separate definitions for griefing and hacking.
Hacking is treated as a much more serious offense and minimum bans in this are are usually in the range of 7days - 21days for first offense, and further offenses result in permanent bans.
Griefing is a very different issue. You already have the ability to prevent others from griefing your own buildings if you use your goldenshovel to claim land. Punishment for griefing is a balancing act between punishments to deter the crime and to making sure its a fair environment and to give people genuine chances. Punishment is also differed on basis of severity of grieifng and other important statistics.
However some of your concerns here are valid and we are overhauling our rules, and creating more standardized punishments.