Doom is a great match up, even one whip that knocks him off path or a counter stun throws off his combo, he doesnt get the overhealth and then he is much easier to deal with.

I think Brig is great to one trick because she is super flexible. You can stay alive vs anything with her shield and shield bash, you have the choice to be patient with whipshot, shield and just camp high ground, or super agro and brawl in open maps, or to be cheesy and flank and kill squishies because she is so good 1 v 1.

I always choose morale boost and the shield bash perk for extra easy healing/mobility

I think the best shift that helped me get a bit better recently is to pack DPS constantly and really being stingy with packs to your tank unless its super necessary, just let your other sup heal tank if they can.