This is tagged as 5th edition DnD, so I'm going to go off of that. I think you may be looking at an outdated source for Kensei monk. I'm looking at the official Wizards Unearthed Arcana:

https://media.wizards.com/2016/dnd/downloads/M_2016_UAMonk1_12_12WKWT.pdf

That source has "Magic Weapons" as you quoted, but has a different feature in place of the "Deft Strike" you're looking at:

Precise Strike. You can focus your attention on a single target in battle to understand and overcome its defenses. As a bonus action, pick one creature you can see within 30 feet of you. The next weapon attack you make against that creature during the current turn adds double your proficiency bonus to the attack roll, rather than your normal proficiency bonus. Once you use this ability, you can't use it again until you finish a short or long rest.

As for the feature you're quoting, I'd agree that it seems underwhelming and inefficient compared to other options. The only benefit I can see is that it allows you to burn Ki points to deal more damage per turn, at the cost of long-term damage. This would usually be inefficient and a poor decision, but if you're ever in a scenario where you need something dead right now, I could see an extra 1d6 per turn being worth considering.

I'd agree that it seems underwhelming and inefficient compared to other options (e.g. Flurry of Blows) in most cases. The only benefit I can see is that it allows you to burn Ki points to deal a burst of extra damage, at the cost of long-term damage. This would usually be inefficient use of resources, but if you're ever in a scenario where you need something dead right now that extra 1d6 per turn could help kill it faster.

This is tagged as 5th edition DnD, so I'm going to go off of that. I think you may be looking at an outdated source for Kensei monk. I'm looking at the official Wizards Unearthed Arcana:

https://media.wizards.com/2016/dnd/downloads/M_2016_UAMonk1_12_12WKWT.pdf

That source has "Magic Weapons" as you quoted, but has a different feature in place of the "Deft Strike" you're looking at:

Precise Strike. You can focus your attention on a single target in battle to understand and overcome its defenses. As a bonus action, pick one creature you can see within 30 feet of you. The next weapon attack you make against that creature during the current turn adds double your proficiency bonus to the attack roll, rather than your normal proficiency bonus. Once you use this ability, you can't use it again until you finish a short or long rest.

I'd agree with you that the feature you quoted would be an inefficient use of a Ki point. Perhaps you are looking at an earlier playtest version of Kensei monk, and they later changed that for the Unearthed Arcana release based on feedback.

This is tagged as 5th edition DnD, so I'm going to go off of that. I think you may be looking at an outdated source for Kensei monk. I'm looking at the official Wizards Unearthed Arcana:

https://media.wizards.com/2016/dnd/downloads/M_2016_UAMonk1_12_12WKWT.pdf

That source has "Magic Weapons" as you quoted, but has a different feature in place of the "Deft Strike" you're looking at:

Precise Strike. You can focus your attention on a single target in battle to understand and overcome its defenses. As a bonus action, pick one creature you can see within 30 feet of you. The next weapon attack you make against that creature during the current turn adds double your proficiency bonus to the attack roll, rather than your normal proficiency bonus. Once you use this ability, you can't use it again until you finish a short or long rest.

As for the feature you're quoting, I'd agree that it seems underwhelming and inefficient compared to other options. The only benefit I can see is that it allows you to burn Ki points to deal more damage per turn, at the cost of long-term damage. This would usually be inefficient and a poor decision, but if you're ever in a scenario where you need something dead right now, I could see an extra 1d6 per turn being worth considering.