Cool, so by level 6 the cleric gets a bonus that a fighter gets at 1st and the paladin and ranger can get at 2nd. Bit of a snorefest as well. It's just not very inspiring.
Actually I was talking about the level 1 blessing of the Forge ability to make the armor magical and give a +1 bonus to AC, since people were complaining about it being useless come 6th level when everyone has magical weapons. I was pointing out that it does not lose it's usefulness because you can always place it on someones armor and not everyone gets all magic weapons and all magic armor even towards the higher levels.
But, if you want to talk 6th level abilities, then note that the Soul of the Forge ability also grants fire resistance, which tieflings get at level 1. So, a Tielfing Paladin who chooses to go with the defensive style who wants to go full defense will have an AC of 23 at level 2 (PLatemail, shield, shield of faith, defensive fighting style) and fire resistance
Forge Cleric can match that at level 1 (PLatemail, shield, shield of Faith, Blessing of the Forge) barring the fire resistance unless they are also a tiefling. Then surpass it at level 6, getting an AC of 24
We could also talk about how Divine Strike is essentially a second weapon attack, which the fighter and paladin get at 5th level.
Now, I completely agree with you that the ability is not flashy or exciting. Honestly, if I had one big complaint about the subclass it would be that most of their abilities are passive "make my numbers bigger" type abilities. But, +1 AC is always strong, no matter when you get it, which is why it is still a good idea to take defensive at 10th level as a champion. Or why getting +1 armor or shields is still useful.
Boring I can give you, but let's not start saying "this class gets the same thing first" because those debates don't mean a lot when comparing a full caster to a partial caster, because the spells are always in the background making up the difference.