The difference was you could do the challenges at any point you wanted to and didn't even need to think about doing them. Here you only get 3 (4 with premium) that you have to seriously focus on doing to unlock the next set of challenges.

If there was an achievement for killing 50 enemies from a distance to save a teammate then nobody would care because that would just happen naturally over hours of gameplay. But now that there's a challenge for killing 5 enemies from a distance to save a teammate it's frustrating because you now have to sweat to do something that has such a small chance of happening. And specific challenges like that are the only way to move up in the battlepass after a certain point.

It's engineered frustration designed to make you either spend cash on levelling up or on challenge swaps so you get an easier challenge.