Yes, this skill is essential to power level. Yes, it's over powered, but who cares really. This is way better than the unopened soda bottle trick. The facts in the post focusing on increase the deadliness of the skill. There are additional things you can do to augment this skill, but it's out of the scope on this guide. Check out Land decimator in action and all of it's glory. Here it's being used to magic extract and shard farming. Nice multi-tasking happening in this video.
You can combine it with an Insta-Kill Evility
A lot of people don't know this, but you can get the added benefit with the Fatal Slash Evility. This Evility is obtained from the Rabbit class. The Fatal Slash Evility has a 30% chance to deathblow enemies with a lower speed rating. This works extreme well with enemies with a slightly lower speed rating than you. You can adjust the difficulty factor to exploit this. Please keep in mind that this doesn't affect your accuracy.
You can perform multiple attacks per turn
The Twin Dragons Evility will allow you to attack twice if your character doesn't move. The idea is to take your Sage out of the base panel and fire away. Because the Sage didn't move, you will get to attack twice. You can either pick up the Evility as a Sage, or you magi-change a monster with it. I have had a lot of success with Izuna and Drumdawn. Izuna magic changes into a staff and Drumdawn has the twin dragon Evility.
The Sage also has a skill named Multi-Attacker. This skill is unique. Unfortunately you can share it will other classes. Just create a few characters of the Sage class and that will allow you to stack attacks.
Max Hit Rate is 50%
You can do a lot of damage using this skill, but the hit rate is capped at 50%. There's not much you can do about this. This is baked into the skill. Just use skill that multiply your number of attacks.
Using this skill is the best way to power level. Take a little time to explore it. It took a while for me to make it deadly, but with a little effort you can make your Sage's Land Decimator deadly too.