Short of being a lawful good paladin, or a grey maiden, there seems no general way to build a Dwarven fighter who is a walking tank of Armor. The fighter maxes out proficiency a Master.
Now I recognize that the play test has a lot of stuff left out and that it doesn't need to be able to cover every concept, but without a base class available to all alignments that get to focus on Armor proficiency, the only way that any characters are getting to be legends in heavy armor look to be through archetypes that tie them to specific narrative elements. I imagine that Hell knights will and probably an order of dwarven defenders so it will open up a little, but the general cavalier archetype doesn't even get armor options, which means that legendary heavy armor proficiency is incredibly gated.
Is this the point? Is heavy armor supposed to be tied to being a part of some organization that provides it? If so, then it seems like Heavy armors should all be uncommon at the very least.
And if the answer is, well fighters can do it well, I can see how that is true, and letting the legendary weapon class get legendary armor for free would over power them as the martial paragons at high levels, but there should be a defensive tank build that does not require an alignment gate.
It seems like the fighter cannot be legendary in armor by default because that's the Paladin's schtick (much like how no one but fighter's can't be legendary with weapons, including monks with unarmed strikes.)
Probably the way to do this is with prestige archetypes, though the gray maiden one only applies to one specific armor and has other restrictions which make it not a good option for "here is the way you get legendary with armor" dedication. We could probably print a bunch dedications which grant legendary proficiency with specific armors or weapons (e.g. Aldori Swordlord granting legendary proficiency with the Aldori Duelling Sword, once those are both things.)
I get that, but shouldn't the paladin's thing be more closely linked to them being divine champions, with powers that make sense to be gated by anathema and alignment?
Best at heavy armor having that gate (or requiring other narratively specific restrictions) is a steep hit to a lot of different character concepts.
I think it should be abundantly clear that the playtest lacks options that the final version will have. For example, it is currently impossible to have legendary proficiency in medium or light armor, which is almost surely not the permanent state of affairs.
But since the Paladin is the iconic "knight in shining armor" class, it makes sense they should have the shiniest armor without additional investment. We just need an avenue for "additional investment" to allow characters to be the best at any number of things.
I think the no legendary light armor is a pretty intentional developer desicision. It is unnecessary for high dexterity characters, as it would allow them to have absolute top tier ACs without any of the penalties accrued by heavy armor wearers. It becomes the superior option at Legendary proficiency. And I agree that the general lack of options is a play test reality that doesn't bother me. What bothers me is that there is actually no path for a general armored hulk character that isn't bound by paladin alignment restrictions, IF legendary Armor proficiency is supposed to be limited to only one base character class and that class is alignment restricted.
Dwarven heavy armored defender is not a character concept that should require a specialized archetype to work.
Maybe the long term plan is for there to be a PF1 style archetype for the fighter that lets the fighter switch to the Paladin Armor progression in exchange for toning down their weapon proficiencies, maxing out at master and moving the level it is acquired back...but that frame work does not look like it exists in what we have seen in the play test.
So one thing we're missing in the core rules definitely is "higher level ancestry feats".
I could definitely see higher (i.e. 9+) level dwarf feats which make one better in heavy armor. Could definitely see one which doubles the unburdened bonus, and another one (level 17?) which requires heavy armor mastery and gives legend?