D&D 5E - Heat Metal Spell. Unfair to Heavy Armor Wearers?

It has a range of 60 feet. Which will be relevant to this conversation.

It does 2d8 fire damage each round the caster uses a bonus action to cause that damage. It lasts for up to 1 minute. So over 10 rounds that's about 90 HP damage.

The spell is frequently cast on PCs wearing heavy armor. Heavy armor cannot be removed within the 10 rounds, even with help. There is no save to avoid this damage for armor you're wearing (there is only a save to hold onto a weapon rather than drop it.)

Here's the key: The spell does not specify you need line of sight, or need to stay within range, during the duration. And the rule for that kind of spell in the Player's Handbook is, "Once a spell is cast, its effects aren't limited by its range, unless the spell's description says otherwise." There are some spells which do include in the description that it ends if you move out of range, such as Witch Bolt which says, "The spell also ends if the target is ever outside the spell’s range or if it has total cover from you." But spells like Heat Metal don't include that kind of description and are similar to the Sleep spell where, once cast, you just stay asleep even if the caster leaves line of sight or range.

Which means a caster can just cast this spell on someone in heavy armor and just run away. As long as they expend a bonus action every turn while they flee, the target will eventually take 90 HP damage from this second level spell. They could even teleport away. I think they could even go to another plane of existence and the still would continue to do the damage for the full minute?

The reason I think the spell might be unfair is because it's particularly damaging to PCs in heavy armor. Yes, of course it could be used by a PC on a foe, but the odds of running into a foe in heavy armor is typically pretty low. Most casters who can prepare the spell, choose not to because they go too many days without being able to use the spell as effectively as other second level spells.

Which means this spell is more often used by enemy spellcasters. And it's most often used by them against PCs with heavy armor, if they're around, because they cannot remove that armor in time to avoid any damage.

It's already not particularly optimal for a PC to wear heavy armor given its cost, strength requirement, speed reduction, stealth reduction, fact that you can't easily wear it while long resting, etc. Players who make PCs with heavy armor are often already doing it for aesthetics and could have possibly made a slightly more effective PC focused on Dex instead (even if it's just a 14 Dex and medium armor). This spell is often, by the circumstances of actual play, likely punishing those heavy armor Strength based PCs further for being a Str based PC in heavy armor. And I don't like that.

How do others find this spell to be in their games?

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