There is no logical or lore-based reason for any of the Iso Vaults to be gated behind each other.

[(XBOX)TehChubbyDugan]

Of the 3 original Iso Vaults, all of them play out exactly the same, with very minor exceptions to a few numbers and the drop tables themselves.  Absolutely nothing about the mechanics of the vaults or even the lore we have in-game for them suggests a sound reason for why you have to open vault 1 to open vault 2 to open vault 3.  There is no reason for this other than DE wants to extend grind by making you do arbitrary tasks before you can do the grind you want to do.  There isn't any more sense involved in what is here than if they required that we first run a capture mission on Jupiter to access Vault 3.  

Then there's the fact that the patch on PC has new grind gated behind old grind, meaning you have to do even more mechanically unrelated tasks just to grind out new content.  These all need to be separated into individual vaults/bounties that can be farmed separately.  Not doing so is just admitting that you don't have a reasonable amount of content in your patches and have to resort to underhanded tactics like this to artificially extend grind.

You already didn't touch the laughably bad Necramech mod drop rates or do more than a pittance of QOL on necramechs and have barely provided a reason at all for anyone to be interested in these things.  You Monkey's Paw'd the hell out of us with nearly every single concession to player's wants for changes.  Every patch feels a little more spiteful toward players than the last did, like someone at DE's feelings are really hurt that the community doesn't like a lack of QOL and expects content to not be gated behind ridiculous, tedious grind, instead of the content and replayability of that content standing on its own.

There's still a lot I like about this game, and a lot of fun to be had, it's just that none of it is on the Cambion Drift and that's a pretty big issue.

[Leqesai]

I completely agree.

Each of the three locations should be its own thing and have their own necramech/rewards based on the current tier system

Locking them behind time-gating is horrible game design.