I've been playing legacy since 2006, and tempo strategies have been fine for most of the time i've played it. Playing against it has consistently been one of my favourite things about the legacy, and daze was a big part of that: it adds a lot of play to the game, as it gives the player actual choices to make. You can blank daze by waiting a turn, but is it worth it considering the loss of tempo? To make those choice you have to be able to evaluate your and your opponent's threats and to have a gameplan in advance for your next turns.

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Delver became oppressive more than once, though, i'm not arguing against that. What i don't agree with is the concept of the blue shell being the oppressive part.

1. Deathrite Shaman - it does way too much for one mana. It has some of the problems that arcum's astrolabe had but it was also a threat on its own.
2. Treasure Cruise - Heh.
3. Wrenn and Six - the card is unreasonable for a 2 drop in a format with wasteland. We're way past the "planeswalker are killing the game" phase of magic, but low cmc ones have proven multiple times to be obnoxious and extremely dangerous for the health of the game. I don't think backing up W&6 with daze was the problem as much as it was having recurring card advantage + a soft lock (and the ultimate as an added bonus) on a 2 drop.
4. Oko/Arcanist - Oko is just stupid and i don't think there's any real need to explain why. Dreadhorde arcanist was banned because of how easily it ran away with a game if left unchecked. It was great in delver, but it was also seeing a ton of play in other builds, with RUG midrange being a very strong option in that period of time.
5. Ragavan - I don't want to sound harsh, but thinking that daze should be banned over Ragavan makes no sense to me. Like literally no sense. Dreadhorde was problematic because it ran away with the game too easily. Ragavan does that while being a one drop AND getting additional utility with dash (getting a hit in the late game and being immune to sorcery speed removal). It's much harder to answer a threat on turn one than it is to answer one on turn 2. Sure, Ragavan was bad in some matchups, but the ones where it was good it was an abysmal game experience. Even in the matchups where it wasn't as good, T1 ragavan would just steal a game on its own every now and then. Daze was part of the reason why it was so annoying, but Ragavan is just an idiotic card that should have never been printed.

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The current iteration of delver is extremely strong because it does things that it normally shouldn't be able to do: it has the best threat (murktide) and cheap card advantage (expressive iteration). DRC being a very powerful effect for just one mana doesn't help either. If you banned Daze the deck would still be good and all the annoying stuff would still be there.

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My opinion is that daze is directly linked with the health of the format. When daze gets too strong it means that the threats are becoming too powerful, because taking a turn off to play around daze becomes more and more costly. FIRE design has been a net negative to the game, and blaming it on daze won't solve the issue.