As much as I’ve enjoyed Delves, assuming they (or something comparable) will be a part of the game going forward, I’d want this major change for the sake of longevity and continued interest: allow Delves to be completed with the Follower(s) of your choosing, with scaling commensurate with bringing an additional human player (or players) along with you.
As it stands, Brann sucks in a myriad of ways and forces gameplay that is really out of whack with nearly everything else, battle-wise, we experience. Given how many followers some of us have accrued when they were a part of WoD and Legion, and how those followers have distinct classes of their own (following the same DPS, Tank, Healer trio), allowing us to replace Brann with any of those, or turning a Delve into a quasi-follower dungeon with the appropriate scaling, seems to be an easy fix.
It would incentivize players to return to old content and acquire some of those followers. It would add a breath of fresh air in terms of the playing style of Delves. And it would allow for gameplay that’s consistent with other content, instead of having to fight against the enemies of the delve AND Brann being a colossal idiot a significant portion of the time.
Even if you don’t go that route in terms of allowing Brann to be replaced by Followers from previous expansions, at least create dedicated Brann-like companions who actually function comparably to classes in the game. A Tank companion that actually uses tank abilities like a Druid, DK, Warrior, or Paladin would. A Healer that uses direct heals instead of throwing healing potions on the ground. A DPS that knows how to avoid AoE and when to interrupt.
Given that other, older games had solved this issue relatively elegantly (such as FFXIV and The Old Republic), keeping Brann as he is just screams laziness, while not significantly adjusting the toolkit of the classes who have to work around Brann’s inadequacies regardless of role he’s playing.
As it stands now, Follower Dungeons are essentially DoA, the followers we accrued back in WoD and Legion are collecting dust, and Brann is suffering from a terrible case of CTE.