Not an attack here but what is your experience with 5e?
Plate armor is stronger than all of the magic armors currently in the game. In AL (Adventurer's League - WotC's organized DND play league) it is impossible to get plate before late tier 2 (around level 8, usually later).
Not OP, but in most of my PnP 5e campaigns - both official modules and homebrew - Plate Mail is usually acquirable around levels 4-6, notably earlier than level 8. I agree with OP that Plate Armor (or at least Splint Armor) should be available in BG3, around the same time the 3rd tier of light/medium armors are. Plate Armor
should be stronger than corresponding available versions of lighter armors.
Here's roughly how I think it should go (armor weights - light, medium, and heavy - are separated by |'s)
Level 1 ---- Tier 1: Leather Armor | Chain Shirt | Chain Mail - Dex modifiers of +3, +2, and n/a give total AC of 14, 15, and 16
Level 2-3 - Tier 2: Studded Leather | Scale/Breast | Splint -- Dex modifiers of +3, +2, and n/a give total AC of 15, 16, and 17
Level 4-6 - Tier 3: Studded Leather +1 | Half Plate | Plate -- Dex modifiers of +4, +2, and n/a give total AC of 17, 17, and 18
Level 7+: Increasingly magic versions of armors
Even if you don't agree with my exact level examples, in BG3 at level ~4-5 we can purchase both Studded Leather +1 and Scale Mail +1 (both are Tier 3 Armors in their weight category). And Half-Plate (again, Tier 3) is available from the start if you steal it from Lae'zel. Thus, it's only fair that we have the ability to acquire Plate Armor. AT THE VERY LEAST, we should have access to normal Splint Armor, either via merchant or findable while exploring/looting. But Larian seems to think that heavy armors should be reserved for mid-late game, which strongly nerfs str-fighters.
Either Larian should add more heavy armors to the game, or they should remove some of the more powerful available light/medium armors.