Not a fan of season journey rewarding build-specific items

Personally I don’t care what other people do. But I still reach the same conclusion as you do.
It is about which meaningful options the game is giving me as a player. And if it hands me one choice that is just much better than other choices, well, yeah, that is bland and boring.

But why have that boost?
Like with many other changes, it feels like Blizzard is removing the actual game from the game. Finding new gear that makes you more powerful is essential to Diablo. When you get the Gift Set in D3, a major part of that specific gameplay loop is ripped out of the game. You instantly are moved toward a place where you will find less upgrades, due to the massive skip you just got (since less drops will have a chance to be an upgrade now).

Likewise, in D4, the time in the entire game, where gear upgrades are most meaningful, is early on in WT4.