Monks have a lower damage than all other classes Talisman Gold by design. This means though you can tank the big bosses easily, it will take a very long time in killing them yourself. This is especially bad in those scenario bosses those have AOE, area damage hitting multiple people, damage and you do not have ranged damagers with you. A shovel can reduce this disadvantage greatly but in many scenarios, you will need to use the staff in order to get aggro, this means that the you need higher enemy value, so that the boss hits you and not your team mates, especially when you have high damage dealing team mates. For this reason, it is recommended that a monk keeps both a staff and a shovel.
Tanking can become boring at times. With a staff, you only have to press one button (Fatal Bash) to damage as well as keep aggro. This is a little boring in my opinion. And the low damage will make you yawn before you kill a boss.