I've always felt that the dwarf's ability to ignore speed reduction from armor is a bit of a red herring, or perhaps a holdover from 4th edition that has lost its purpose because of the way the armor rules changed. It sounds like a kind of cool little benefit, but when you really look at it, it doesn't have much application in the game and would require an inordinate amount of effort to get any benefit.
The dwarf's speed entry says the character's speed is not reduced by armor; but armor speed reductions come from wearing heavy armor without having a high enough Strength:
Heavy Armor: ... the armor reduces the wearer’s speed by 10 feet unless the wearer has a Strength score equal to or higher than the listed score.
The only classes that inherently have heavy armor proficiency are clerics (some domains), fighters, and paladins, which are all, to a greater or lesser degree, strength-focused classes. Others can gain it through a feat, or through a slightly oddball multiclassing scheme (starting with a heavy-armor class and then changing course from level 2 on to focus on the class they really want to be in).
So what kind of characters benefit from this ability? If you're any good with weapons, you either have high strength and don't need it, or you have good dexterity and don't need it. (Medium armor gets you the same AC at a lower cost, and if you would need a feat to gain Heavy proficiency, spending the feat on Medium Armor Master is a better choice.) If you didn't start with at least Medium armor, getting the Heavy proficiency would require an inordinate number of feats or some multiclassing gymnastics.
So it seems to me that there are only a few types of characters who might reasonably use this benefit:
- A cleric who ignores strength in favor of wisdom, to enhance their casting.
- A dexterity-focused cleric/fighter/paladin who really wants to wear plate armor. (Though dex-focused builds generally don't actively choose dwarf...)
- A valor bard who is bad at weapon combat.
Have I missed an obvious character archetype that would find this ability useful? Or is it really just relegated to a few corner-case character concepts?