I think the DCI should have a laissez faire approach to the B&R list. If we go back to the Chalice or Lodestone ban, it seems that it was made because of people complaining about "fun". I don't think either should have been restricted because they were shop's answer to blue card advantage (you can disagree with me on this). I have some pet cards that I would love to play again (restrict revoker + ballista please for Goblin Welder), but I don't think we should use personal preference to determine the B&R. Now, some people think that we should because at the end of the day, Magic is a game and a game is meant to be fun. I respect that opinion, but I disagree.
What's fun for one person is not the same for another. As a result of it's subjectivity, I think the default, purest way to go about the B&R is to go by objective "brokenness." I don't think Gush was fun. I think it's stupid and boring. However, I don't think it was inherently "broken" either. It canabalized blue, yes, but it also got WRECKED by thorns. If we go to rock-paper-scissors of pregush restriction, i'd argue that big blue > shops > gush > big blue. The issue was that people enjoyed gush more than big blue, despite the poorer shops matchup. This lead to people who play big blue to feel bad because they have to face more gush decks than expected. However, that's an issue with preference, and not "brokenness."
tl;dr I think the B&R should be used for brokenness, not fun. One man's trash is another man's Goblin Welder.
And to be clear, my post may be incoherent because i'm tired AF from studying. I'm also a Goblin Welder fanboy so the whole Gush vs. Mana Drain discussion doesn't really bother me as I would play Mishra's Workshop regardless.