Wowwee
This isn't just a conspiracy theory, it's a conspiracy theory that's based on a poor understanding of how the universe works. Finding things suspicious when they're absolutely expected. When crypto went mainstream what did you think it would look like?
All your points can be simplified into two parts,. the conspiracy and the question of what happens if Ethereum goes down.
The second part would be a valid question except not in your case. No one can prove to you that it can't happen by explaining the technicals because you aren't asking a technical question. Anything you can be shown you can say the "bankers" only made it to look that way. After all you've already had to use that logic to even consider this a reasonable idea in the first place.
Just think for a moment... You're saying that in order to defeat Bitcoin/cryptocurrency, the Bankers crafted a cunning plot where it would create a revolutionary system that would skyrocket cryptocurrency into exponential growth and uptake. (not to mention all the Ethereum-like systems since) Essentially you're saying Ethereum is SO GOOD for crypto, it must be a nefarious super villainous plot by the people who want to destroy crypto.
What do you think would have happened without Ethereum?
If you accept that it would only be a matter of time before someone else developed a similar system to Ethereum then obviously you'd need to explain how you'd tell the difference.
If no one else would have ever come up with anything like it then crypto's rise could never have got to what we're seeing now. That's what the banks want, right? So why would they give everyone the plans/idea for this technology?
Essentially even if the "bankers" really were as bafflingly insanely stupid as this (yet are also super genius'!" and they did press a "nuke the ethereum" button. you'd still find they'd end up with a net loss with crypto's aftermath stronger than it would have been without it and now even more strong after it recovered. It would be one of the most self defeating idiotic ideas ever.
The end goal is to restore their control of the money supply. If that happens by crypto skyrocketing or failing doesn't matter as long as they get what they are after, control. You tell me I lack understanding but you have no concept of how boom bust cycles have played out historically to create to engineer just the situation I described in order to grab control of the market and then have it skyrocket. That is not a theory, that is historical fact, and it will happen again because it works.