I agree with all of your points, except on Boromir.
I would say that what Boromir needs is better tank abilities to enhance his role as a tank. Here are my ideas:
Final Stand: Make this ability activate when Boromir is at 5% health, giving him a temporary 999% armor boost, while keeping him in control of the player. In addition, this ability should become stronger incrementally at levels 3, 5, 7 and 10, making the debuff last longer and making the armor boost last longer. If these changes were implemented, Boromir would become incredibly resistant to damage for a short time, while also still being attackable, due to not being invulnerable. This would force enemies to fight him and suffer a nasty debuff, or run. I will also note that Gondor is 1 of only 2 factions who have no means of debuffing their enemies, which hurts them terribly late game against most factions.
Horn of Gondor: This ability is underwhelming to say the least. With the sheer amount of fear resistance in the game, it becomes utterly useless after 10 minutes in the game. My suggestions would be to decrease the cooldown of this and all other stun fear effect abilities to 30 seconds to counteract temporary fear resistance buffs. It also needs an additional effect so that it can be somewhat useful after the enemy gets a fear resistance source, so cause it to also slow enemies down, maybe halve their speed.
Brave Resistance: I'm ok with this being a straight armor buff for Boromir, it should not give any damage. I, however, have a different idea. This could be a passive ability, similar to Celeborn's, where the more surrounded by enemy troops Boromir is, the more armor he gains. Starting at 25 troops he gains 50% armor, and then 25% more for every 25 enemies up to 500, for a total of 525% max if 500 enemy troops or more are nearby. This would represent him fighting against huge amounts of Uruk-hai in defense of the hobbits quite nicely I think.
I have no issue with Boromir's 2 other abilities, but the first 3 definitely need some more oomph to make them better.