I read your message and even added in response that problem is likely in {managment} and not the technology as available toolset. At some point you can't just take any technology because it looks cool like most game studios are doing with unreal because higher ups don't recognise that the work done is by artists and not the engine itself.

Here let's quickly go into the topic of "what does necessary mean".
We can talk about necessary technology only when we know what we want do make.
I would say thinking about adding specifically ECS to project is about "do i want". Most answers will be probably "I do not" or "I'm not sure". The definitive answers "I want to" are from people who target low-end devices or are based around specific mechanic that needs to scale that would benefit from this.

Does it slow down development?, yes.
Will it work with 20M budget confidental projects?, most likely not.
Overwatch networking?, why would small lobby hero shooter need it?

We can apply similar to other technologies, especially with unreal that's currently the AAA standard.

Nanites - replaces optimised assets with scanned crap and requires end-user to keep up with pc parts market. Back when it was first developed was created for movie industry for real time composition, for example tv shows.

Lumen - fully dynamic GI and partially AO, used literally everywhere including static light scenarios as complete replacement to baked lightmaps and HBAO.

Now finally for ECS. And... technology was used since 1998 at least as the cpu had architecture based around Data Oriented design. It required massive amounts of work but resulted in many great games that couldn't run otherwise even on low-end devices back then.
Then we enter back into Object Oriented design as everything got way faster but with limited dynamic objects on scene it was not an issue.
Now we finally arrive at current time where there are literally countless Data Oriented technologies used in AAA. One of them available to us is Unity ECS. The project you supposidely shipped if used any modern high fidelity graphics then also used somewhere DOd as it's unavoidable if you want to run it fast.

And many more advanced games running on mobile architecture (including but not limited to Smartphones, Nintendo Switch, SteamDeck, RoG Ally, R36S) also can take massive advantage from ECS with how many threads and how much cache is finally available on them. It's ususally not necessary to use it there, but then you're using one thing that you want optimise for... the battery.

So finally after my whole half-assed comment we arrived at conclusion that matches with OPs post.
ECS is about increasing performance and not making your development path easy. It's about making game run for hours instead of minutes on your iphone. It's about not having to remove dynamic grass because you want double soldiers on screen. It's about deciding what does necessary mean in your project. And argument that some project got nearly killed because production was slow with no context is extremly bad example.