War Machine & Master Architect worth it?
Quick video explaining the pros and cons of the War Machine & Master Architect set that give you the Major Slayer buff with boosts your damage by 15% for 10 seconds in Dungeons & Trials.
I do not recommend it for Magicka setups because most of the times you are using a high cost ultimate and therefore you will only get a very low uptime. Unless you are a Magicka Templar that uses Empowered Sweep which only costs 75 Ultimate Points.
Stamina Setups have access to very cheap ultimates like Dawnbreaker which makes the set more powerful. You will get about a 30% uptime on Major Slayer if you use Dawnbreaker (from Fighters Guild Skill-tree).
Especially for Warden healers this can be a very useful set combined with the Healing Tree Ultimate. Keep in mind, that you will have 1 less Aggressive Warhorn in the group if you choose to run the Healing Tree Ultimate. You could also use the Resto Staff Ultimate if you want to use the set on a non Warden healer.
I do think that Warden tanks can use the set pretty well if there is no better alternative and then boost the damage of the melee players by a fair bit. You can almost get a 100% uptime on Major Slayer when you have enough Ultimate regeneration and you using the Healing Tree Ultimate. But be careful, that means you will have 1 less Aggressive Warhorn in the group.
How does the buff work?
Here is the biggest problem with the set, when you have two people using the set and they activate the ultimates at the same time, it overrides each other. The buff system does not check whether a person already has the buff or not. It just targets the two closest people, even if they already have the buff from another person.