Okay, here's the thing: They never really were necessary. Most of them were actually pretty useless, too. As far as getting set up goes, the good ones never took that look to find the parts for and build. You're REALLY exaggerating things.
In tranzit, the turbine was all in one room. Pretty much the same with the shield, the most worthwhile buildables.
In Die Rise, okay, I'll admit, the trample steam was a pain to put together. Sliquifier was meh, but the parts were near each other.
in MOTD, relatively near each other, AND you could pick em all up at once.
in Buried, it was just a pain to sort em all out, but none of em were really necessary to build. Regardless, it hardly takes an hour when you know what you're doing.
In Origins, you had the 2 buildables and the staves. You don't really need to get all the staves, and the other two aren't difficult to find parts for.
I just find it funny how you say this stuff is necessary. None of it is necessary, except the turbine in tranzit really. You can play in whatever way you so choose. You don't HAVE to build everything. You do not need to get the one inch punch and stuff like that. With that said I agree that there shouldn't be as much locked down in the easter egg (and that the EE shouldn't be so in your face). It's just, don't act like you have to have everything to survive. You don't.
Honestly if you want to get far in zombies that is it's main goal you do kinda need the wonder weapons and you need to upgrade them. In Black Ops II imo it just took way too much time to set everything up before you could actually "play".
Then lets go through em again
Tranzit- Doesn't have a good one
Die Rise- Parts are in the same room
MOTD- Box gun, or optional from the EE
Buried- Box gun
Origins- This is the only one I'll give you. Building the staves themselves isn't necessarily an issue (and you don't really need to get em all to upgrade them), but the upgrading is a pain in the ass.
IMO, the set up is actually the best part of the game, because it isn't just running around in circles killing zombies. It's building yourself up. There are some cases where it gets tiresome, though. In particular, Buried. It's basically just waiting for the booze to spawn to keep going forwards. Everything else, though? Fun. I think some people forget that they can keep going through rounds while doing some of the objectives. Risky? Maybe, but it's more fun than running around in circles all day.