dnd 5e – Improving terrible spells: the sword of Mordenkainen

In my response to "Does the spell of Mordenkainen's sword have little power?", I came to the conclusion that the spell is terrible. Critiquing a spell is one thing; improve it is another. Then, can the sword be fixed, or is it condemned to rot in the spellbooks forever, so as not to be copied?

First, the original:

Sword of Mordenkainen

Evocation of level 7

Audition time: 1 action
Distance: 60 feet
Components: V, S, M (a miniature platinum sword with hilt and copper and zinc knob, worth 250 gp)
Duration: Concentration, 1 minute.

You create a sword-shaped force plane that floats within range. Duration lasts.

When the sword appears, you make a melee spell attack against a target of your choice within 5 feet of the sword. In one hit, the target receives 3d10 force damage. Until the spell ends, you can use a bonus action in each of your turns to move the sword up to 20 feet to a place you can see and repeat this attack against the same target or a different one.

Mordenkainen Sword It has several notable problems:

  • Sword damage is bad for a concentration spell. For three rounds (assuming all attacks hit), the sword causes 66 damage, while Bigby's hand deals 108 damage (when reversed to level 7).
  • Sword damage is bad for a non-concentration spell. Crown of stars of Xanathar lasts one hour and does not require concentration, but still makes 78 damages in 3 rounds.
  • The sword is inferior to the non-damaging options. Why waste a level 7 slot inflicting (terrible) damage to a single target, when you can put most creatures in a forcecage without saving? The 20 foot movement of the sword in each turn also means that it can not reach mobile high level enemies, such as dragons.

Mordenkainen Sword It also has several features that make it unique:

  • The sword is the highest level spell that targets a single creature, requires concentration and only causes damage. Even if we relax the concentration requirement, only crown of stars (also level 7) meets the remaining requirements.
  • The sword allows two attacks in the first turn, but only one after that. Taking out the early damage is usually better than splitting it into multiple turns, but this can complicate attempts to rebalance the sword.
  • The sword is one of the four wizard spells that only require a melee spell attack. The others are vampiric touch, the faithful dog of Mordenkainen, Y steel wind blow.

My goal is to maintain what makes the spell unique, while solving your balance problems. Keeping that in mind, the spell remains the same, except for the second paragraph and the new "at the highest levels", which now says:

When the sword appears, you make a melee spell attack against a target of your choice within 5 feet of the sword. In one hit, the target takes 7d10 damage of force. Until the spell ends, you can use a bonus action in each of your turns to move the sword to 60 With your feet to a place, you can see and repeat this attack against the same goal or a different one.

On higher levels. When you cast this spell using a spell slot of level 8 or higher, the damage increases by 2d10 for each slot level above 7º.

Increase base damage, movement and damage to higher levels. Mordenkainen Sword Is it balanced as a damage spell from a single level 7 target that requires concentration?