First of all, I am sorry you lost money because you were tricked into downloading a fake piece of software. I would like to highlight that your were tricked and misguided. Let's now take a look at what went wrong and how to share the blame.
I see this as a fundamental problem with the wallet.
If was a problem, but it has now been rectified. Such server messages can't be sent anymore.
I was sent an error message during a transaction, it asked me to update the wallet.
Surely, this has to be a the electrum wallet's fault!
How can this be my fault? I was in the electrum app, the message appeared in the app.
Electrum's fault was allowing such messages to be displayed to those connected to malicious nodes. That shouldn't have been possible because we as users, don't need to be reading messages from those owning Electrum servers. You fault was not checking where that link leads. If you did, you would see that it directed you to a site that is not the official Electrum site. You downloaded and installed Electrum from an unofficial website. That's your first mistake. The second one is that you didn't verify the installation files you downloaded. If you had done that, the verification would have failed because the app wasn't signed by Electrum's real developer.
The electrum wallet blockchain was hacked - I followed the instructions sent to me by the app.
The blockchain was not hacked. Electrum wasn't hacked. Malicious entities took advantage of a feature that allowed them to make messages visible to those connected to their servers. The message wasn't sent to you by Electrum. It was sent by those who were hosting Electrum nodes.
I received no warning or prior knowledge (at the time) of this kind of thing happening, - you would think that a warning message would be front and centre when conducting transactions.
Unless you got affected early on before Electrum became aware of the problem, the developers did post information about the issues on their homepage. You just didn't see it.
Is electrum ever going to do anything to help those poor people who got duped through what I see as completely their fault?
Electrum is not a for-profit company that makes money on your use of their free and open-source applications.
so why didn't the developers have a notice front and centre warning people, or even freeze transactions until the problem was rectified?
They could have done that, and I agree with you on that. As soon as you opened the app, you should have seen a warning of some sorts that there is an on-going phishing campaign, and that you shouldn't trust or click on links that instruct you to download new software updates. When it comes to freezing transactions. Electrum is a non-custodial wallet. That means they don't have access to your keys or ways to prevent you spending your coins. They could have blocked all servers, making Electrum unavailable and basically a dead app, but what would be the point in that?