Bethesda did go to id for help with Fallout 4 though, id did almost all the work on the weapons and gunplay.
Yes, you read that right, literally the only good thing Fallout 4 has over it's predecessors was fucking outsourced to another developer.
I heard the GECK was actually decent, you're right, however, in that the game's absurdly low level of replay value hampers creativity immensely.
You can't do alternate starts anymore, you can't add new perks or traits thanks to the shitty animations and limited space on the perk tree, can't really define your build because skills are gone, can't be evil because Bethesda didn't write in any additional paths aside from the linear heroic route, can't mod in new companions because the PC is voiced, can't mod in any new quests because the PC is voiced, can't mod in any new factions because the PC is voiced. The voiced protagonist fucked things so hard that it pretty much sinks the game, as I knew it would the moment it was confirmed. No new dialogue options open up based around your perks or skills, something that even Fallout 3 had, as shitty as it was implemented.
The only thing that kind of extends replay value is the fact that it has multiple factions to choose from to finish the game, but even then, none of them seem to meaningfully impact the ending in any significant way, since only one slide can change.
Beth made nearly every wrong decision the possibly could to actively sabotage the potential modding support and replayability of the game, and that's not even talking about the Beth.net shenanigans with fucking consoletards stealing mods like a bunch of stupid kikes.
Fallout 4, thankfully, was the game that broke the camel's back for a lot of people from what I've seen. Still a smashing success, but with a more mixed reaction than any of Beth's previous titles.